Uh, how do you know A + B have hands? You have a marginal hand and you think the preflop aggressor is weaker than you. You are putting him on a continuation bet. This isn't a clear fold, absent a strong read on A and B, it's a clear raise! If you limp call, A + B get in for one bet with some very good odds. If they call or raise the 2 bets, now you have something to go on. Now is the time to begin thinking about getting away from your hand.

If it was heads up, it would be a raise and not a call as well. Is C making a continuation bet or does he have something? If you call, you get nowhere closer to finding out the answer. If you raise and C is weak, well you've put him in a pickle, haven't you?