You are listening to tabloid gossip. William is not a muslim. Charles has made an ass of himself pandering to muslims, but is not a muslim. Diana was sleeping and partying with a playboy who was from a wealthy family of muslim background (there are a lot of them in London), but that didn't make her a muslim -- she also slept with a lot of wealthy Englishmen, and their family ties to Christianity hadn't rubbed off on her, either.
Harry and Meghan did their share of pandering to muslims before departing UK, but don't appear to be leaning eastward as of now. I wouldn't put it past them if their publicity dries up, however.
As for the muslims "claiming the cross", I have no idea what you mean by that. They recognize Jesus as a major prophet, but do not believe He died on the cross, or that He is the Son of God. Source