Hero: 15.5BB UTG
Villain: 25BB capable of squeezing. Also knows shove ranges fairly well

Hero opens UTG with AJo. Button and small blind flat (~12k in pot) BB shoves all in. Should hero call off remaining 13BB with AJo in this position. Knows for sure that button and small are folding so only have to worry about villain. Also reason for opening on a 15.5BB stack instead of shoving is because there are roughly 5 players with less than 18BBs. Plan on folding to a few of them because they are only butted when shoving. BB however is capable of shoving here with 77-AA as well as KQ+.

1) Wrong forum

2) As usual, it depends on info you haven't provided. In particular, what is your table image and what is your relative advantage/disadvantage in skill against the remaining players.

3) Kind of an oddly structured tourney where, at a final table, a player raises and there are two callers plus the BB and the pot size is 12K.

4) I would not have opened AJo in this spot. Once you do, there are 6 hands that have you dominated, a couple realistic hands which you dominate, and the rest are close to coin flips with you being a small underdog in the vast majority of them. So the question becomes, are you prepared to put your tournament at risk facing those kinds of odds? If you are, then you call. If not, fold. One thing I would add, though, is, by opening UTG with such a short stack, you are representing a good amount of strength. If the BB is capable of putting more than 60% of his stack at risk in that spot on a pure squeeze with a hand which does not have you dominated, or is at least ahead, then more power to him/her.