AF web site do not mention the possibility to bring a (paying) guest for Siver members, so I don't think it's possible. But you have nothing to loose to ask the lounge dragon.
For your other question, op-ups from Y to PV happen if Y is overbooked and some seats are available (or can be made available) in PV. For your specific flight, it's impossible to know that in advance. But it's better for you to not expect anything and maybe have a nice surprise