Plus One Invitation Dilemma!

The number of reserved seats and specific names on the invitation are perfectly fine. Definitely not rude, especially because you're including all spouses and serious relationships

Plus ones are for only truly single people. The ones you mentioned should be included as a social unit anyhow.
Just do it like you've planned, only address it to the guests invited and the we have reserved __ seats is perfect! And be prepared to say no a bit if anybody tries to add someone!

I agree with PP

What you’re doing is fine. You don’t need to say that seating is limited, seating is limited in every venue.

You could do 'we have reserved _ seats in your honour' or I recently got a wedding invite that had a separate little card that said the couple would love to have everyone there but due to venue restrictions only those named on the invites could be allocated. I thought it was a nice touch and meant that it wasn't written directly on the RSVP card.

Thank you all! I think we will just put we have reserved X amount of seats

I don't think there is any polite way to exclude someone's significant other because you didn't consider them "long term" enough for an invite. I wouldn't worry about single guests, it's not standard they get a plus one. I would address the save the date and the invite to the specific person invited. Then on the RSVP card, put "___ out of ___ attending" and fill out the second line with the number invited. In my eyes, "plus ones" are for nonspecific guests a single person can bring. A significant other should always be included & invited by name, even if they haven't been together very long.

Don't say seating is limited - just name the invited guests. I think the "2 seats reserved in your honor" method is good.

Invite guests that are in a relationship (length of time not your call or your business) get invited together by name. If they are single - there is never a need to invite them with a plus one.

You need to specifically indicate how many of the invited people are planning to attend.

i.e. __ of 2 or whatever the number is so that there’s no “misunderstanding”.

Be prepared for backlash. My nephew and his now wife didn’t give plus ones to anyone in a relationship less than a year. Their excuse was limited space. They then decided to do a B list of invitees and would extend plus ones based on declines, All this backfired on them. People were pretty peeved about the whole thing (rightfully so) and they ended up with far less guests than expected. It’s never a good thing to disrespect other’s relationships when you’re inviting them to celebrate yours.