Consider how awkward it would be for any of your guests not to be invited by name, directly and personally, but to be relegated to the second-class status of “guests of guests.” That is why none of your guests should be invited as “and guest.”
Couples are invited as couples; singles are invited as singles. If a single person is in a serious romantic relationship and you want to include that person’s friend, then you ask the single for the friend’s name and contact information and send another invitation to that person. If you are not fully convinced that your guests should be treated equally as guests, then consider how much it will trivialize the occasion of your daughter’s wedding to treat the reception like a nightclub for which “dates” are required so as to have a good time.
This of course simplifies your concern about the wedding celebrant. Just send him an invitation, made out in his name alone, to the wedding reception. If he attends, that is lovely and it will be up to him to figure out how to mingle with the other guests. (Although, since a priest should be treated as an honored guest, you could seat him at the same table as you and your husband, where you can make certain to engage him in social chatter if he seems not to have anyone to talk to.) If he cannot attend, he will let you know. But, in any event, you need not worry about inviting anyone to “keep company” with him.
