Legal Question in Criminal Law in Michigan

There are separate issues here: the man's risks and the woman's risks. Although you don't say exactly, it sounds like one probation condition for the Assault CSC defendant is to not have contact with minors under a certain age. If he does so without approval by his probation officer and/or the judge, he risks a probation violation that could put him back behind bars. (This is not an unusual probation condition to lower the risk of him repeating his past conduct of sexual misconduct.) He wouldn't be prohibited from marrying (unless the fiancee is the Assault CSC victim, in which case the probation order might specify her as someone he must not have contact with). Yes, the defendant has constitutional rights to freedom of association (which includes his right to marry this woman) ... but if this conflicts with another legitimate public interest (e.g., protecting children from risk of harm), then his individual right can be trumped while he's on probation. The woman's risk is not with the criminal case's judge, because the judge doesn't have power to order her to do things ... but her risk is with folks like Children's Protective Services, which might be contacted with someone who is reporting "a guy on CSC probation and on the sex offender registry living with a lady and her little kids". If the mom is allowing conduct or conditions that puts her children at an unreasonable risk of physical or emotional harm, CPS might get try to get involved with the family, a neglect petition might be filed in the family court, etc. Although YOU (or the girlfriend) might think that the guy is not guilty, that the guy is not a risk to the girlfriend's kids, others who look at things more objectively might disagree.