What's the call?

[Nevadaref]

The question of which T to assess is a good one. Here's my take.

Since you did not observe #21 come back onto the court, you don't know if he did it while the ball was still dead or if he came on during play while the ball was live.
Therefore, the only call that is supported by the rules here is the TEAM technical foul for having more than five team members participating.

The illegal substitution T which would be charged to the individual needs to be observed as he enters during a live ball. If he simply walked off and then came back before the throw-in began, he really shouldn't be penalized for illegal entry/substitution because he may not have been the player who was actually supposed to leave. That's a kid/coach being confused. As long as the ball hasn't yet become live that can be sorted out. However, once the throw-in begins, the TEAM must be penalized. NO WAY should an official stop play and then continue at the POI without penalty as suggested by a previous poster.