We stay two in a studio all the time. Even with multiple showers a day (we usually go in July/August), we've never had an issue with towels. It's just a matter of hanging them up to dry after each shower. Getting them changed out only on cleaning days doesn't ever seem to be a problem for us.
We do laundry a few times each stay to reduce the number of things we need to pack, but I can't say I've ever had to wash a Disney towel -- even when we're in a larger unit with its own laundry machines.
If you do find the towels to be an issue, you can always use one of the "pay as you play" housekeeping services:
- Towel Package, $6.00 - 4 bath towels, 2 hand towels, 4 washcloths, 1 bath mat
- Additional Full Cleaning of a Studio - $30.00 per day
- Additional Trash & Towel Service for a Studio - $15.00 per day