Two things:
Does trouble seed work on your partner in 2v2?
Yes, haven't tested personally but I have the PBR guide and it shows that one opponent uses ability-affecting moves to create monstrous Slaking and Regigigas.
and
If you send out a pokemon with a power item attached in a random battle and then switch to something else to do the fighting (faint opponent), does the first pokemon still receive the bonus EVs (i.e. fight bidoof with HP power item = 5 EVs)? Does this stack with pokerus like normal (bidoof + power = 10 EVs)?