Animation the involves two game objects

I’m really struggling to find some resource that talks about this.

How would I do about using animations that involve 2 game objects or more?

For example:
Human grabbing a door knob or pushing a door.
Two humans handshaking. Or any sort of interaction between two humans (ex. high five)

Any starting point would be really appreciated.

Thanks!

A little late

Research IK controls in Unity. That will get you started.