Hey,
I'm just gonna reply on your first question, because i'm not a 100% sure about the second.
But to answer your first question, i think it depends on what you select in your tactics for that game for "substitutions".
For example, i you selected "let coach decide" or "coach pics from depth chart", well then your coach can in theory choose any player he wants from your depth chart, to replace your backup PF, which is not necessarily your reserve PF, but could be again your starting PF like you had.
On the other hand, i think if you would have chosen "strictly follow depth chart" or "dept chart until 4th", i think you reserve PF would have ended up playing more minutes that only 1.
grtz,
eagle