Can the seller counter two or more offers?

First, it's legal for a seller to counter two or more offers, but it's not wise. The seller could potentially be bound to sell their home to two or more potential buyers if the those buyers accept the sellers counteroffers. I typically advise my seller to reject the offers and simply ask for "highest & best." It's also not uncommon to completely reject one offer and "counter" the second. Especially if the first offer is completely unrealistic.

It's important to remember that when someone makes an offer or counteroffer they give the other party the power of acceptance to create a binding contract.