I think it really depends on you and your family.
Plenty of people go on vacation and put four people into a studio and do fine. I had a friend in high school who had five brothers and sisters, his parents and grandmother, all in a house that couldn't have been over 1,000 square feet and had a single bathroom - and they lived that way every day, not just for a week.
But a lot of people feel cramped with the kids in the living room. A lot of girls that age won't want to share the pull out couch. Some people solve the bed taking up the entire room problem (along with the "I don't want to sleep with my sister" whine) by not using it and putting the kids on aero mattresses on the floor.
Its a trade. A two bedroom with your daughters would be great - but do you have enough points - or enough money? Will it require you to shorten your trip? If you can afford a two bedroom without it impacting something else that's a priority (i.e. not being able to eat anything but beans and ramen because of the add on, or only being able to stay for four nights rather than a week), get the two bedroom.