This has been a constant struggle for us as we plan. When I first asked my FMIL for her list she gave me very few names. I kept asking if that was all, telling her and my fiance that they could invite more people and stressing that the list would help us decide on the venue. I encouraged them to add more people because it is easier to cut than add.
At the end of the initial guest count phase we had 150 people on the list. Only 30 or 40 of them were his family. We picked a venue based on the 150 guest count and moved on. Then we changed venues to a more comfortable place in September (indoor reception vs outdoor) that happened to be larger... then all of a sudden my FMIL had more people to add to the list. This didn't make me happy because we never would have booked the first place if she had just added them from the get go. But her list balanced out my family so I added them, plus a few more friends now that we had the room. New guest list 196.
Now, we're now 100 days from the wedding and planning invitations. She had let me know that there were some more people she wanted to add and stressed that she would pay for their food. She told me these people were my FI's dad's relatives from out of the country. Originally she wasn't going to invite them because she didn't think they would come, but they've started to ask about dates to book flights so she wanted to invite them. This pissed me off because I told her to invite them from the get go. She said that she thought at most it would be 100 people total from my FI's family. My family is at 80 people. It seemed reasonable, so I gave her the current list and asked her to add them.
She just called my FI and informed us that she would like 65 invitations for her family. The current count is 30. This means that her guest list is more than doubling! This is more than just the Canadian relatives! But I don't even know what the final number is because she hasn't even given me a count, just the number of invitations she wants. By my estimates this means that our guest list has ballooned to 260 at the minimum!
I told my FI how frustrated I am about the changes and he replies, "These are people they wanted to invite but couldn't when we were constrained to the smaller venue" OMG that isn't even reality! We never would have looked at that venue if they just put them on the list like I asked them to! She's offered to pay for their dinners, so it's not about money- it's about the fact that we're 100 days out and people who were not important 101 days out are now suddenly on the list. My FI wants them to just be added because his parents want them there, but I'm pissed. Between my mom not talking to me for the past two days because I want to put my FI's parents names on the invitations and this I'm getting pretty sick of parent shenanigans.
/Rant