More than one mandatory substitution

[Scrapper1]

I looked through my casebook and couldn't come up with a definite procedure for this situation, which was presented to me today by a fellow official.

A1 drives to the basket and is fouled by B1. A1 falls awkwardly and the trainer comes on the floor to attend to him. Team A has no time-outs remaining. The foul is B1's fifth personal foul.

Both players must be replaced by rule. Is there a right/wrong way to do this? Do we:

1) Wait until A1 can be moved from the court and then handle the substitutions or get B1's sub while A1 is being tended to?

2) If we wait for A1 to be moved from the court, do we replace B1 first (20 seconds) then replace A1 (20 seconds) or vice versa; or do we replace them during the same 20 second interval?

Now change the original scenario just slightly. Team A wants to use a time-out to keep A1 in the game. Do we replace B1 immediately and then grant A's time-out? (I think we do this.) Or do we allow Team A to use its time-out to fix A1 and then resume by getting B1's sub?