Guest List Out of Control

Is anyone else's guest list getting out of control? Although, my parents (who are paying) say it doesn't matter who or how many we invite, I feel like my FH's side's guest list is out of control. His mom swears that she knows over 120 friends of the family will for sure show plus his family plus any strays. My mom & I only rented 150 chairs!!!! Now my mom is suggesting we up it to 200. FFIL says that they all won't show, but FH and FMIL both swear all these people will! I feel like people should be limited to plus ones but then where will people leave their kids! ((The guest list is over 400 people including kids and plus ones.)) There's even people on the guest list that FMIL doesn't even know their last name! Plus, I feel horrible asking my parents to pay for all these people.