There are different branches of Shaykhis and each branch has different beliefs, so it’s difficult to generalize about their beliefs.
If they believe in the following:
1- The Ahlulbayt are creations of Allah and they are slaves of Allah
2- They reject Tafwid
3- Allah has empowered them to create and give sustenance
It doesn’t mean that they are deviants. Yes, some of our scholars might state there is no valid evidence for these beliefs, but if some believe there is evidence for it then it’s not kufr to believe in them as long as they don’t ascribe independent powers to them. As long as they say Allah gave them those powers then it’s not kufr and one can pray behind them.