Two Questions Regarding Combat Phase

[Apologetic Canadian]

Hello everyone! Some friends and I finally decided to pick up Age of Sigmar again; however, we've run into two rules we needed clarification on that came up in our game. One can apply to any match, while the second applies specifically to multiplayer matches (so three or more armies on the table).

1. For the 3'' Pile-In, can a friendly unit that was not charged for combat, but is within 3'' of an enemy unit/model in combat, move 3'' and make its attacks as normal? It seems very similar to Heroic Intervention from Warhammer 40,000; however, being able to do that as any unit most certainly left us puzzled.
2. In a multiplayer match, how do units activate in combat? As an example that came up today, Player A charged into Player B and Player C's units. While Player A was able to take their first combat, Player B then responded... and we didn't know if Player C would activate and have it go back to Player A, or if it would go back to Player A right after someone retaliates. We also weren't sure how it would continue if the combat went into the next player's turn - will Player A and Player B activate and fight again in Player B's turn, but Player C waits until their turn for Player A and Player C to activate? Does everyone involved in a combat, regardless of whose turn it is, activate in the combat phase?

Needless to say, the confusion from #2 made us decide to, for the moment, give up on multiplayer games until we have a better idea on how to handle things. Anyway, your responses and guidance are greatly appreciated.

[AverageBoss]

1. Absolutely. If they are within to pile in, and can get into weapons range doing so, they can attack. Some models even have 3" reach and would not even need to pile in to attack. Combat in AoS is full alternating activation on a unit by unit basis. So the player controlling that unit could simply activate it like any other when it swings around to his turn to do so.

2. Once again full alternating activation's in turn order. Player A would activate any eligible units on the table, then player B, then player C, then repeat unit all eligible units have activated.

[JackStreicher]

1:  yes.

2: Play triumph and treachery and the issue won‘t arise.

[BaldoBeardo]

Just as an aside, the only way a unit can be within 3" of an enemy unit is through charges or previous piling-in by either unit - you can't just wander up to an engaged enemy unit and then pile-in, for example.