Would the following Shadowblade and Greenflame Blade combination be legal?

Let’s say I am a level 5 sorcerer and I have already cast Shadowblade. And I want to do the following on my next turn:

Quicken Greenflame Blade for 2d8 (from shadowblade) + 1d8 (GFB dmg) on the main target and 1d8 + spell mod on the creature next to it.

Then as my action I Twin the GFB again and I make the first attack on target 1 and second attack on the target next to it which allows me to do basically double dmg from above calculation.

Is this allowed by RAW? If not why?