Sub Question
 

B1 is DQ for 5 fouls. B6 comes to replaces B1. Can I bring in A6 at this time before the second free throw?

Thanks, Bud

Yep.

Yes,
Rule 3-3-c During multiple free throws resulting from personal fouls, subsitutions may be made only before the final attempt in the sequence and after the final attempt has been converted. Exception: When a player is required by rule to be replaced prior to administering the free throw(s), then all other substitutes who have leaglly reported may also enter the game.