fh Family inviting more people. Please help!

The good news is he already opened the door for the conversation where FH calls him and tells him, unfortunately, his daughter and grandchildren are not invited due to guest list limitations, but you're hoping he can still attend. Hold firm....

I invited my mom's half siblings but not their children for multiple reasons (we were over numbers already, I've never met them, between the three siblings they have 14 children, etc) These were people that I said "99% sure they won't come" due to distance and financial reasons. Well my mothers half sister (I've met her maybe twice in 23 years and we do not speak) messaged me on Facebook and tried to guilt trip me into allowing her kids to come. It wasn't just one message either. She sent constant messages about how her kids needed to meet me and my mom for 45 minutes. I was polite but firm in my answer. "I'd love to meet them at a later date but as I previously mentioned, we are at our max capacity." Unfortunately you can't control other people and their lack of manners.

You should feel no guilt whatsoever in telling them no. You can give a detailed explanation or just say, "We're sorry, but we cannot accommodate your request." I don't know why people think it's okay to invite people to your wedding, but it's so common.

Yeah, I feel like people don't assume or know it's rude sometimes. So I've been trying to be gracious about it. How did the half-sister react after you told her no?

Still building up the courage but I think I'm going to tell them today!

She literally would not leave it alone. She'd respond with a "Well they've never even met their aunt!(my mom)" and "They're getting to the age that they're asking about their cousins and they really want to meet you." I just kept saying the same thing and then I managed to steer the conversation in a different direction. She messaged me the next day and said "Good news! We can make it!" Grreeeeat. Then she messaged me the following week and told me they were all going to travel but her husband was going to stay with the kids the night of the wedding so she could come. She THEN asked if I could hang out with them the day prior to my wedding. *facepalm* No. No I cannot. The nerve that this woman has is completely insane.

The fact that he wrote to email him if it wasn't possible tells me that he was prepared for this to not be ok. He's taking a chance that you'll allow it. This is extremely rude, of course, for any guest to make such an assumption, but ultimately it's up to you whether you can afford to, or want to host these "other" guests. I don't think you should worry about offending this uncle, as it's clear he's prepared for you to contact him if it's a problem. You should politely explain that you needed to keep it smaller, so unfortunately you couldn't invite everyone, and have no room for extras. Stick to your list.