If we drove in in an RV is there plenty of room to turn around

The sign before main entrance states "No RVs beyond this point"

You Cannot take RV's passed the first gate, which is clearly marked.

Easily. There are multiple locations where you can turn around.

Yes the roads are very wide and there are at least 5 turnouts before the main area and in the spot by San Ysidro trail you should have plenty of space.

Yes , in the parking lot you can turn around.