I married muiri and I decided to talk to Bothela(is she muiri mother not too sure..) anyway she told me that the sliver bloods give her trouble and that they make Yngvar shake her down for coin. So me being an assassin and the champion of molag bal is there anyway I can hurt the sliver bloods for this? Or at least break Yngvar's legs? Hell I just want to kill them or at least Yngvar.

You can't. They are all essentials

If you do the quest The Forsworn Conspiracy and follow it through to the following quest, you end up weakening Silver-Bloods a lot. You also get an option to kill Thonar Silver-Blood.

Sweet I better get started will this quest weaken the current jarl? He is rather a cool guy to be honest.

If the current jarl is Igmund, you'll probably have another view of him after doing that quest... He's one of the worst jarls IMO.

eh the sliver bloods are no better from what I have seen, eh markath is some screwed up city the only reason why I like is that it has a nice PC house and a shrine of molag bal.