Typically once a seller accepts a contract, the other (or subsequent) offers will be for backup only.
Once out of attorney review, none of the offers can be accepted unless the first one fall apart.
As many as come in! Until the seller accepts an offer and it is OUT of attorney review.. as many as come in.
Once a seller accepts an offer and until it is out of attorney review any offers go directly to the sellers attorney for presentation to the home seller.. it is the choice of the seller at that point.