if you want to help them, and yourself at the same time - biuld your army, ally with the turks, and as soon as the byzantines or fatamids attack one of their provinces and force them into the stronghol, march a relief army into the threatened province.

Provided you have a decent enough force, the enemy will retreat and abandon the province, and the turks will ove you. You'll also up your kings influence stats so good heirs are on the way. I've been doing this with the Volga Bulgar against the People of Novgorod. I like the VB's. Bashkorts and SHC ftw.