I recently did a Najd run and had the same problem but with even stronger ottos and timmies. They had eaten Qara, were allied and both rivalled me.
What I did was wait until the Otto's got into some pointless war with Venice, and then declare war on the Timmies (Or vice versa with Timmies vs Moskovy). With the otto's distracted you can focus your forces on the timmies.
For this to work effectively you need Offensive Ideas, good generals and good use of mountains. Once you have enough warscore demand the alliance to be broken.
Now this might take one or two tries. I remember white peacing once. But if you do it enough, the otto's and timmies will eventually rival eachother.
You do not need to get to a 100% warscore, just break the alliance and then fight them one on one.