How possible is it that i could win guardianship of these kids , FROM A LEGAL STANDPOINT?

Without their consent, they have to be declared unfit parents, the state will step in and you may have the opportunity to foster and eventually adopt if the parents are unwilling to get their act together. Just know that these types of legal issues are very emotional, can be costly and will almost always severe familial relationships. Contact a family law attorney to advise you before doing or contacting anyone else.