We just got back from a hotel vacation with our 2 year old and 3 1/2 year old. It went much better than expected. They were completely exhausted from all the day's activities, so they crashed at about 8/8:30 each night. The only downside was that my husband and I went to bed at the same time as the kids (not so bad for me...I'm pregnant and loved getting 11 hours of sleep each night!!!).
We had one room with 2 double beds. We had my 2 year old in a pack and play and my 3 year old slept in my bed. She loved it! My husband got the bed to himself!
I wouldn't feel comfortable leaving them alone in the room, but mine are much younger than yours. I would worry if someone woke up and was in an unfamiliar place and would be scared.
We kept the same bedtime routine as home...bath, stories, bed. I would recommend bringing some familar things from your child's bed...a sheet/blanket or pillow, stuffed animal or lovey, or something from home. We forgot to bring my 2 year old's Barney doll and he kept asking for it. We felt bad that we forgot his favorite bedtime thing.
Good luck, have fun, and don't worry too much about it! If you don't make a big deal out of it, hopefully they won't either. We were pleasantly surprised (our kids are not known to be good sleepers!).