99 midpair on Ax flop

3-way I would just fold to the turn bet, I can't think of any hands that we beat here. I do not think a c-bet on the flop is profitable here, the board is too draw heavy and there are some weak aces in the villains hand ranges, so the fold equity 3-ways is probably not here.

I am having similar troubles with pocket pairs since in many cases they are not good enough for a x/c call, neither on flop nor turn - in particular not in mwp with A high board.
In general, you could consider cbetting flop in these situations rather then x/c for bluff induce, however as shooshte already mentioned the board drawy and its likely that SB/BB coldcalling range has hit here.

x/f flop & turn is my play here

A Cbet for thin value and protection could be a option if you deal with passive players, but 3 way it's extreme thin.
Turn is for me a easy fold multi way. To often you are facing at least top pair here.

Cheers,
SDK1987