The only significant upgrades are the 5D IV or 5DSR. You won't notice much of a difference going from the 5D II to the 6D, 6D II, or 5D III.
I upgraded from the 5D II to the 5DSR five years ago, and just added the 90D last year. The 90D is fine as my second camera for sports, and despite the 90D's touchscreen, using the 5DSR is far more user friendly.
For typical use when you fill the frame of the 5DSR it's 50MP is superior to the 32MP of the APS-C. When switching to APS-C the lenses you have all shift in the view you are used to. You will also have to add a wider lens to get the field of view of your widest lens. Transitions are far smoother with the 5DSR as well.
The 90D will deliver more detail than the 5D II/III/IV, 6D/II, but high ISO quality will decrease, and getting used to the crop factor for regular shooting would be challenging. It would however make an awesome addition to your 5D II for high speed telephoto photography though. The crop factor, 10 fps, and 32MP, deliver great results for sports, birds, wildlife, and quickly moving grandkids!
I have amazing 24" x 36" prints from the 5D II. It is still a very capable camera, so perhaps adding a 90D for all the above reasons could be very useful for you.