In a place of illusional freedom, as is Germany, law professions which supposed to have the freedom of movement, to pursue their mission, arrive, as well, to get limited by applying the principle of neutrality.
The Civil or the panel law on their own couldn’t stand without procedure rules or procedure codes. In a few law systems, family law is part of Civil law. Modern lawyers tend to follow a particular direction and get extra specialized on that. They get the title like "family lawyer", or "property lawyer" and so go on. In that way, the neutrality of the law, in such a law system, is applied inherently, without specific rules! A lawyer who decides to follow a particular law direction is looking after no interactions with other law directions may occur during his/her law carrier!
In Germany and many modern law systems, I guess, a request for child custody, according to the family law, from a person who did show criminal activity should not be an issue in the custody request!
A mother who uses to keep asking the custody, for her children who got abused by her, even if she committed crimes which include underaged people, does still have the right to an impartial child custody hearing.
The right to start any legal case, submitting any legal remedy must be assured for anyone. This has been one of the law's main principles for a very long time. Securing the start for any legal case shows some difficulties when there are interactions with other open cases. A judge of the Family Court could not secure a free judgment, about a child custody request, if getting permanently interrupted from a criminal case petition during the hearing. The core is to let the Judge work exclusively on his case. Does that, really mean, that an abusive parent should get an impartial hearing about his custody request, requiring no petition of his criminal behaviors?