How to label on my seating chart with guests that has not RSVP-ed

You could make a seating chart for the people who did RSVP and then leave the rest of the table open and maybe say "Seat Available", "Did not RSVP" seems a little rude, however, that would be appropriate because they didn't RSVP.

Is there anyway to get them to RSVP? Can you get addresses or maybe word of mouth can spread that they should RSVP on your website if you have one.

Do you know at least how many people you are suppose to save the seat for? I am doing something like this

What do you mean when you say that the groom's family cannot give you names of people attending. Did you send invitations? Who are they supposed to RSVP to, the groom's family? Why not you?

Call them and ask if they are coming.

Why are they unable to give you a final number a week ahead of time? If there's some kind of family emergency going on, I'd accept that answer and put "seat available" on the place cards. If there's no emergency, I'd call whoever told you that back and let that person know that you need to know by xx date who exactly is coming.

How is your caterer okay with not having a final head count?!

Um, what? Why would the groom's family not be able to give you the number of people attending? Did you not send invitations with RSVPs? Why aren't they RSVPing to you?

You will need a final headcount for your caterer. On top of that, there's no way in hell I would save extra seats for people who couldn't even bother to RSVP to my wedding!

Fill in what you can, and then put the unknowns as "Guest of Mr. ---" with your husbands name.

Also, if you know the relation of the guests whose names you are unsure of, let the planner or catering staff know. When they can't find they're names at the entrance, your hired staff can at least tell them what table.