I think it would be OK to ask, but don't be surprised if the coach doesn't want to give out too much information and decide what you will do if you're not satisfied with the answer.
Absolutely. You should know who your son (and your family) are going to be spending the next year with.
Additionally you want to understand the skill set of the group. That may not be a big deal depending on the age group or the focus of the team (development vs. highly competitive) but you definitely have the right to ask.