Could we have some pictures or a video which shows your method when you try to install the tire ? Sometimes, use some soap might help.
This is the method I've been using for over eight years: first I insert the first side, then the second, using levers if necessary to raise the final part (I've often succeeded even without levers).
I usually use Schwalbe Easy Fit to seat a tubeless tire...I've never had to use it to install a tire on the rim, but I might try.