under which scenario...? Or both?

fold in first scenario. Second scenario, depends on the card. If a jack, i bet, cal a raise and call down, possibly i'm in the wrong for that. If its a spade, i check behind and possibly call river. Remember, you only have second pair and people will play any ace and call down with it.

i think QJo is very marginal with 3 limpers and the blinds yet to act. if the deck doesn't slap you on the flop (yeah baby, i know you like it that way), i would dump it. middle pair with an ace on the board in a family pot is not your friend.

i would want at least two pair or an OESD (or both).

in situation one, i might try to get a free peak at the turn looking for 2pr or better. betting is one possible line, but i have to think that you'r spewing chips when betting into that many people.