Room capacity threads usually get shut down because of heated debates. The official capacity is 4 plus one child under the age of three.
When our youngest son was 4, MS let us make ressies for a 1 bedroom. I asked if we could stay in a 1 bedroom with 2 adults and three kids. They asked ages, I told them and they allowed it. Our ressie said it was for 5.
It really comes down to the ages of the kids. Also keep in mind there is no bedding for a 5th person.
Good Luck!