The participating Pokemon only get experience once. Everybody else in the party gets half of the total each.
Experience gain is independent of participants and number of Pokemon in your party, so yes, your party gains more experience overall if you have more people in your party at the same time.
All pokemon earn experience independently. So the rest of your party does not affect the amount of experience they earn. This is also independent of the Exp. Share's on-state.
I do not know how EV's through Battle work in Gen 6. So I won't comment on their distribution here.
So five example Pancham Battles:
Battle 1a (4 party members):
- Pokemon A participates.
- Pokemon A earned 80 experience.
- Pokemon B,C and D earn 40 experience each.
Battle 1b (3 Party Members):
- Pokemon A participates.
- Pokemon A earned 80 experience.
- Pokemon B and C earn 40 experience each.
Battle Example 2a (Exp. Share On):
- Pokemon A and B participate.
- Pokemon A and B get 80 experience each.
- Pokemon C and D earn 40 experience each.
Battle Example 2b (Exp. Share Off):
- Pokemon A and B participate.
- Pokemon A and B get 80 experience each.
- Pokemon C and D get 0 experience each.
Battle Example 2c (3 party Member Exp. Share Off):
- Pokemon A participates.
- Pokemon A gets 80 experience each.
- Pokemon B and C get 0 experience each.
Traded Pokemon do get boosted experience even if they do not participate.
The Pokemon that have mega evolutions at the moment are somewhat arbitrary, in my opinion. Notably the only starters on the list are the Kanto starters (one of which has TWO versions) and Blaizken, and there are no new sixth generation Pokemon with a mega evolution! According to Serebii this is the current list (and this is believed to be final at this point, as there are no other known mega stones).
Note that most mega evolutions have different abilities, and a few even change their typing!
Best Answer
When using EXP Share, the EV gain is applied to all your Pokemon that gain EXP, so fainted Pokemon will not receive EVs. Pokemon that are holding EV-gain items like Macho Brace or the Power series will received the appropriate increased EVs even if they aren't switched in.