I thought the pot size bet from the MP just showed a little too much weakness, in addition to his preflop limp, hence the call. Was this play okay or when could it be different?

Usually multiple callers on a flush draw flop means one is chasing.

I would have given up on turn after the flush hit.

Tbh I'm folding flop. 4 way flop and someone donks pot size into you on A high board... Rarely are you ahead, and when u are ahead it's not by much. Save your chips.

Plus I would rather guess that pot size bet is not a sign of a weakness on those limits, but rather of a good quality hand (made or strong draw) since maaany people have no clue about drawing with proper odds and how to get value.

Please correct me if I am wrong, I might be.

I'm with my namesake here. If its HU otf, it would take extraordinary circumstances for me to fold TP. Multiway, facing a PSB, I don't think its close really. Once the flush card comes and more money goes in, it seems likely at least one player has at least 2pr.
Best play is a pre flop fold I think.
The fact is at low stakes isolating to 3x is going to very often result in a multiway pot. A6o would be one of my LEAST favourite hands to play in a multiway pot with little fold equity. I would literally prefer to do this with T7s, although I would fold that as well.

Against very loose opponents, which you have here, (I mean look at what hands they saw the flop with), I would ISO at least 4x, and only with a strong range.
With suited playable hands I would actually limp behind (gasps from the poker crowd) and value bet the **** out of people when I make a hand.

Q:As played, aside from a 6 or an A, and taking into acc both blinds may call (the price just keeps getting better with each previous caller) what card are you happy to see on the turn and put the rest of the money in multiway?
You probably see where I'm going with this

Firstly, thank you for such a detailed reply, this is exactly the kind of hand analysis I was looking for.

I think my issue was getting fixated on MP and thinking that I had him beat, I almost disregarded all the other players as I assumed they would fold to the PSB. Definitely a lesson learned about multiway pots.

And completely agree about the turn card situation. At best I'm around 12% (I think) to improve on the turn, and even then in a multiway I'm still likely to be behind somewhere with 2p.