What are the rules of Force Powers and Minions?
The short answer is if you want to affect multiple minions, you would need to activate the magnitude upgrades unless your GM says otherwise.
Taking this into consideration:
What happens if I use the Power Bind, on its basic form, against a
group of minions?
In its basic form, you restrain one minion. In this case, you immobilize temporarily one minion until the end of the next turn. This might affect the skill ranks as if a member of the group was absent.
What happens if I use the Force Power Move to target a single minion
an throw it to another minion, and both minions are in the same group?
You harm both minions with equal damage. Similar to grenades where you can affect multiple targets, you deal damage to the thrown minion and the target minion. If the minions act as a group, the wound threshold is shared but each attack is soaked by armor.
What happens if I use the Force Power Harm with the Magnitude property
against a minion group?
With the first magnitude upgrade, the remaining force point would harm an additional target. If you are targetting two minions, it would deal twice the damage to the group's wound threshold.
As a general answer, I recommend reviewing the current FAQ available in FFG site (v2.0, dated 11/20/2017). For additional examples on Minions groups, I recommend the developer's answered questions thread.
related to force powers and minions:
related to minions and Blast quality (as an example of damaging multiple minions in a group):