Find children whose parents are in the same room

I have two tables ROOMS and CONTACTS. I then have two types of contacts related to each other. Investigator(parent) and Tech(child) . First we assign a Tech to an Investigator. Then assign Investigators to ROOMS. Now we must assign Techs to the room. However I only want the user to see the tech as option IF they are a tech of an Investigator assigned to the room.

Here is what the structure looks likeenter image description here

join_on_tech and join_on_investigator are table occurrences of the same join table.

room_join_contacts is a separate join table than the other join for parent/child

Currently I have a portal set up and and the user is presented with a list of techs via perform find script command. only it shows all techs rather than techs where investigator is in room

how would I go about filtering out techs that do not have an investigator(parent) in the room