Are Graystripe and Swiftpaw related to Tigerstar?

I've read every book. no way but that would be a neat twist

I think they are, Well.. some people say Patchpelt was Graystripe's father, Patchpelt is Leopardfoot's brother and Leopardfoot was Tigerstar's mother.

Well, even Firestar and Graystripe are related, however distantly. Let's see...

Tigerstar's son is Brambleclaw, whose mate is Squirrelflight, whose father is Firestar, whose sister is Princess, whose son is Cloudtail, whose mate is Brightheart, whose brother is Brackenfur, whose mate is Sorreltail, whose mother is Willowpelt, whose son is Graystripe, whose brother is Swiftpaw.

So, yes, in a weird way (or a lot of weird ways), Graystripe and Swiftpaw are related to Tigerstar.