Can two F+ bacteria conjugate?

No, two F+ bacteria cannot conjugate with each other in the classic sense. In bacterial conjugation, an F+ bacterium (a donor with the fertility plasmid) transfers its F plasmid to an F- bacterium (a recipient lacking the plasmid). If two F+ bacteria were to attempt conjugation, both would already have the F plasmid, so no transfer of the plasmid would occur. Conjugation is typically between an F+ donor and an F- recipient.