How can I prevent casters from stealing the spotlight from non-casters?

I have been running a game of D&D and the group is split with two non magic users (Fighter, Barbarian), one quarter-caster (Paladin), one half-caster (Bard), and two full casters (Cleric, Wizard). The game was going rather well as I had started them from level one, however the group has reached level five and the wizard and the cleric have started solving everything which has been making everyone grumpy. Wizard summons are better at tanking than the barbarian and Paladin. Cleric is far better at buffing the party and talking compared to the bard.

I don’t wish to just go, “You guys walk into a dead magic zone. None of your fancy magic works now.” What can I do to distribute the spotlight equally among the party members?

I was asked for examples. For prime example whenever there is a combat encounter the wizard casts alter self to gain a high natural armor combined with mage armor causing the wizard to have an AC equal to the paladin removing the whole squishiness disadvantage. The wizard also has spell focus conjuration and augment summon so his creatures are actually as good as the fighter and paladin during combat situation.

As for the cleric he has the divine metamagic feat focusing on persistent spell so he is able to give out two buffs that last all day long so the bards song bonuses are pretty much negligible.

Can multiple casters combine Flesh to Stone to petrify a target faster?

The flesh to stone spell states:

A creature restrained by this spell must make another Constitution saving throw at the end of each of its turns. If it successfully saves against this spell three times, the spell ends. If it fails its saves three times, it is turned to stone and subjected to the petrified condition for the duration. The successes and failures don’t need to be consecutive; keep track of both until the target collects three of a kind.

Say a wizard casts flesh to stone on an enemy, an orc to make it simple, and the orc fails the first saving throw.

Then the wizards friend, in the same round, casts a second flesh to stone spell on the poor orc, to which he also fails his saving throw. Then the wizards other friend casts a third flesh to stone in that same round on the poor orc and he fails that saving throw as well.

Does the orc fully petrify in that round? In other words, do the effects of the spells starting to petrify the orc stack with each other? He did fail 3 saving throws but it was against 3 separate spells instead of one spell.

Does the Spirit Guardians spell stack with multiple casters?

Recently played with a group, where 3 of their clerics would cast spirit guardians, claiming monsters in the area had to make 3 wisdom saves for 3d8 damage each, potentially adding up to 9d8 damage per round.

Is this any different then trying to have two casters cast insect plague or cloudkill on the same area, or bless on the same individual?

If a Spell has a casting time of 1 minute, what part of the caster’s action economy would it take up if it was cast in combat?

This is a bit difficult of an idea for me to articulate, so I’ll try and do my best: If a character was to attempt and cast a spell with a casting time of 1 minute, while in combat, would they have to simply consume their action for 10 turns, but still move and take bonus actions? Would they be unable to do anything except cast that spell? Would they also be required to maintain concentration?

How to deal with moderately armoured and shielded casters?

Background

I am DMing Princes of the Apocalypse for 5e. My past campaigns (mostly 3.5 and 4e) were always quite challenging and tough, my players got quite paranoid, and understandably so.

At level 4, all casters (a warlock and a bard) chose moderately armoured as their feat, and now carry a shield and medium armour for an AC of 19, +4 AC for a single feat. But this means that they are tanks, and the supposed front line melee characters all have a lower or the same AC as the ‘squishy casters’. Lowest AC in the group is 17.

Which is fine by me, but the encounters from the adventure are too easy for them now, as the casters are never really in danger because of their high AC. Unfortunately, most encounters from the book have a majority of physical attackers. The higher miss chance for monsters made fights too safe, and take too long, as the players were understandably hesitant to use limited resources (higher level spells, per-long-rest abilities) when not really in danger.

When we discussed the issue of too easy fights during a break and I suggested that I would ad-hoc beef up the encounters for this session, the player were fine with it. And I did, but now the session is over, I am planning the next one and I would like to know:

How to best deal with moderately armoured casters 5e?

Bad options that I see that I do not want to use:

  • Modify the encounters (more casters, traps vs abilities, etc)

    • Problem: Takes time, especially in a location-based, non-railroad adventure.
  • Simply give +attack to Team Monster

    • Problem: Unfair – they should not be punished for clever choices.
  • Disallow Moderately Armoured

    • Problem: I don’t want to force them to rebuild their characters.

How can I best keep the fights interesting while respecting their character creation choices?

Whats happens when a caster’s soul returns to his polymorphed body by the effect of Magic Jar?

Consider the following sequence of actions:

  • A caster casts Magic Jar and his souls travel to the chosen container
  • The caster manages to possess an NPS’s body. The caster’s class features are retained in the new body, together with the original WIS, INT and CHA scores.
  • The caster in the new body casts True Polymorph on the original body and transforms it into a dragon (for example)
  • The caster makes is soul travel back to the original, polymorphed body.

Now, what happens to the casters’ class features? Are they retained? Is there any difference between this course of actions and simply casting True Polymorph on self?

In 13th Age, are the Bard and Sorcerer spontaneous casters?

In 13th Age, casters know all the spells of their class, and have a number of slots determined by level. They can swap their spells every day or after every Full Heal-up. But they need to place that number of spells in the slots.

I can’t find whether the Bard and the Sorcerer, who were spontaneous casters in other d20 games, can keep the slots free to decide in the moment. My guess so far is that they can’t, because normally, nobody can cast the same spell twice, and nobody can allocate the same spell in two slots.

Am I blind or are there just no more spontaneous casters in 13th Age?

Are there rules to create Troops of casters?

So a person I play Pathfinder with showed me the Troops sub-type which opens up a whole lot of possibilities for high level parties to deal with high numbers of enemies.

But I don’t find much about how to deal with Troops composed of caster characters.

Let’s say that a high level party (lvl 15) is attacking an evil wizard school, and they could end up fighting through dozens of low level wizards.

Of course a GM could always just add 20 level 4 wizards to the mix, but honestly, it would be TERRIBLE to manage that combat for the GM, it would take days for the players to act again, and rolling all those possible saves and ranged touch attacks would be just not fun at all. And that’s not even mentioning that a 4th-6th level wizard would probably not be able to do much to a 15th level character unless the player rolled a 1 on their saves, and that has 5% chance of happening.

So I think the immediate solution would be to implement something like a Troop of wizards.

Are there any rules or guidelines for such a thing?