Have just started playing live MTTs, not sure if I made right decision last night.

$50 ~80 player live NLHE deep stacks MTT
Not close to bubble, 400/800/800 SB/BB/BBA
My image is probably tight as I've had no hands in the 2.5 hours of play
Table is generally loose at betting and calling

SB >34BB
BB >34BB
Hero 34BB, 27k
MP1 >34BB
MP2 12BB, recently made a ridiculously tight fold instead of calling with final 12.5BB (showed cards)
MP3 >100BB, table leader, very loose caller (eg C-C pre w T6)
CO >34BB
BTN >34BB

Preflop: Hero UTG w AQo
Hero bet 3.5bb (not sure why I made so big, prob didn't want a lot of callers)
MP2 all in 12.5bb
MP3 call 12.5bb
fold to Hero
Hero? Pot 31bb. Call will give pot 40bb and hero with 21bb behind.

I think I'm ahead of MP2's range, happy to call if MP3 hadn't called.

But what is MP3's range? If I was in his place, and trying to range hero, I'd guess 77+, AJ+, ATs+, KQ, JTs+. Possibly tighter. I think this whole hero range has to at least call the 3bet whether MP3 calls or not, and is then pretty pot committed. So MP3 has to have at least 33% equity against 2 opponents. But note his loose calling, and who knows if he's even thinking about ranges and equity, probably not based on his previous calls.

If you think this is an easy call or AI based on read on MP3, I'd be interested to know what you'd think if MP3 was a decent low stakes player.

BTW, is there a better place to post this, or a good tool to nicely display a live hand? PT4 doesn't seem to do.

Trivial rejam. Live with the results. Sometimes MP3 will be at the top of his range, it's poker
You can't flat call ever ever ever. Shove or fold
Against your description of MP3, I shove all day

If he was a decent low stakes reg, he will never flat call vs MP2 shove ( he will know that MP2 is a funplayer)
He will shove over the top with 66+ AJs+ AQo+

At time I thought can't call but, in retrospect, I had the odds to fit or fold if I wanted.

MP3 decent reg should shove that range w >100bb and other stacks >50bb still to play?