My mind is going to quit my body. C#

By now I figured out the fact that I must be extremely stupid.

Imagine this:
A number of masses.
(blop blop blop) - kind of the sound the masses make when they’re imagined.
These masses are instantiated and scattered.
That is, they just also happen to have random positions.
And rotation!!!
That means that I can never know how they will instantiate.
What I want to do:
Imagine mass 1.
Considering Gravitation , I have the amount of force calculated, and thus Omega (Radians per second).
I consider gravitation from all masses, that is, mass 1 is affected by 2,3,4,5 etc, and vise versa for ALL THE REST.
(After like 6 masses the game is already CPU heavy, because the complexity rises like a boss for every mass)
Now , If I want, for simplicity, just imagine two masses.
Random Rotation and position.
I want to use RotateAround, to Rotate Mass 1 around Mass 2, and vice versa, depending on their also random masses , thus different exertions of force.
Now, the thing is, I can’t tell how the rotation will be.
So it gets harder to use RotateAround.
I can’t use Slerp for gravitation, it looks really FALSE.
Also, I can’t define from and to, as that is always on the GO.
How can I mathematically define a general axis for rotation?!
I don’t want to go the easy way and just give them all equal rotation, or make them all lie on a common plane.
I want it to be realistic, and I am ready to take every measure, BUT I can’t simply comprehend it!
Like if the masses have a rotation of Mass1.transform.rotation , and Mass2.transform.rotation etc, how can I somehow manipulate that, to give a realistic axis of rotation for gravity?
HELP, it is a matter of stupidity or death!

Check out Quaternion.AngleAxis.