A bit late to the party, but I'm a Molinist and can at least attempt to answer here.
First of all, it is important to establish that creating free creatures represents God imposing restrictions on himself; this does not limit His sovereignty or power or any way. In the same way, it does not limit His sovereignty or power to say that He cannot do that which is logically impossible: He cannot make a rock so big he cannot lift it, he cannot make a square circle, and he cannot directly force a free decision.
Given this, let's revisit A, which I would phrase as:
A: There is no possible world in which all people freely choose Christ.
It is at least possible that this is true as a result of human freedom; no matter the world God creates or circumstances He places His creatures in, at least one will not accept Him. This is one possibility, and it would not diminish His sovereignty or power, since it was His choice to create free creatures rather than determine everything.
There is at least one additional possibility, which is that although there are possible worlds in which all come to faith and are saved, none of these worlds exceed a population of X (where X is some tiny number like 10,000).
If God, before the creative decree, was choosing between a world in which none were damned but only 10,000 came to faith, or a world in which many were damned but millions upon millions came to faith, it seems quite reasonable that He might choose to create the latter. In other words, although B may be true, it does not necessarily follow that God would elect to create such a world, since His desire may be that the greatest possible number of people be saved.
TL;DR - Either could be true, but neither is particularly problematic for Molinists. If A is true, free will is a limitation God has placed on himself so that's fine, and if B is true, God could still have reasons not to make such a world.