‎السلام عليكم Ustadh, someone I know, her father passed away, and the male members of her family are fasiqun (they do not pray). Can an imam or a sheikh be her wali?

You can not take away there wilayah so simply as that means you sre announcing them by name to be disbelievers, and this is a very dangerous thing. Your wali is the next of kin otherwise seek a mufti and give him all the details of your case.