Seating arrangements

If I were you, I'd tell your FMIL that you appreciate her help and will get back to her later when you have your RSVP's back and have figured out the tables (round or rectangle). I only included my FMIL in the seating chart because I felt bad that I hadn't included her so far (otherwise I would have never asked for her help).

Sounds like your MIL seems to know everyone your inviting including her guests. Does she want to get married and send out her invites for vows renewal?

I know you are the right ones (yourself and FH) to do the seating plan upon receiving the RSVPs.

She really needs to stop overstepping her boundaries and let down easily said her thought is considerate, yet its just doesn't seem right. Your FH should have a talk with his mother and really know how he feels about her doing this over him and you. Hopefully she does understand and stops her ways.

Yeah I think just explain to her that you can't really decide the seating arrangements until you have a better idea on your numbers. BUT...I'll just say this...that its kinda nice that shes helping, because I'm pretty much going to tell our parents to decide the family and their friends tables, and its never too early to start thinking about how you'll group everybody. Makes it easier later.

Also...just because shes started without you, doesn't mean that you don't have final say on it. Think of it as a suggested seating arrangement lol

At first I was like What?? but after reading the other responses and taking out the emotion of thinking she was overstepping, it might come in handy when you do make your final seating chart. I would ask her if there was a particular reason why she set it up like that or could there be changes made if need be.

I had a meeting with my venue where we laid out a rough floor plan and I'm already stressed about actually doing a seating plan!! I'm not going to seat people until I get RSVPs back because I find it'll ruin the seating plan if I take people out and try to figure out who to put in their spot

I'd let your MIL know that while you appreciate her help, that you'd rather keep the seating planning until you get your final numbers/RSVPs in. Definitely keep responding with smiley faces if she pushes it

I would let her know that you appreciate the help, but you are unsure what the table set up is going to be.

Maybe do a couple plans before your final numbers to see what will work out and then go from there.

Ask her for her plan, and take into consideration the groups she has put together and let her know you will try to make this work after getting final numbers

I would keep sending her smiley faces - and then when you do have the head count and can decide on how many people per table you can let her know. Theeeen when/if she sends another chart for the correct number - you can thank her and let her know you will do your best to keep those groups of people together.

However, if you are looking to mesh the two families together - maybe mention that to her now and she can group them in lower numbers?

Seating charts are one of the most complex parts - dealing with people you may not know well and dynamics that you may not be aware of. There are probably reasons she sat certain people together or apart. I'd suggesting using the recommendations as a tool to help you get to a finished chart. If your seating and tables don't match with her suggestions then move them around but it sounds like a handy starting place to me.