I don't agree with that cyjeff.
A common law marriage is something that only exists in theory until the point that a court rules that a common law marriage was in fact created. But a court can look back in time any number of years and determine that a common law marriage was formed at some point when the couple was co-habitating, even if the couple separated for many years after that. In fact, that is how most common marriages are established. (ex: After separation one party asserts that they were common law married at some point, so now seek divorce and a settlement of "their" property, even though they haven't been living together for years.)
So... this friend of yours may or may not be common law married to this woman but the Court supervising her probation is not going to be making that determination anyway. The answer to your question is that you just have to look at the written terms of her probation to see what she can and can't do, and she can't argue too much about it because she agreed to those terms when she accepted probation. Most probation judgments prohibit the probationer from fraternizing, or certainly co-habitating, with persons of "ill repute" which definitely applies to convicted felons. The terms may specifically prohibit contact with convicted felons. Usually courts will waive this condition as it relates to certain family members, but it is up to the Court. She can petition the Court to make an exception for this man that she considers to be her husband. It will greatly strengthen their argument if this man has any kind of a legal duty to support these children such as a custody order a legal right to see them, such as a visitation order. Her PO really should work with her on this issue and get the issue heard by the Court. If the PO doesn't want to help then she may just have to hire an attorney or try filing a motion herself.