@miyako19
There is no law that prevents a man to live or breed with five girls. There is a law against polygamy, yes, but that comes into effect only if he legally marries all of them. But if he marries only one of them on paper, he can sleep with all of them and make babies with all of them. There is no law that prevents this, he can even register all the children as his children.
The only problem such arrangements may cause are:
1) Custody, which him having made babies with the other sisters may make him be seen as unfit to have custody.
2) Morality clauses in companies, where his choice of lifestyle may cause him to be discriminated against in employment.
3) Bigamy, but this requires one of the girls to bring him to court.
4) Housing, in some jurisdictions, owners can legally limit how many people are allowed to live there.
5) Medical issues, where there may be cases where only direct family members are allowed to see them, but since he's not married to the person, he's not considered as family member and therefore barred entry. I can see this as a problem when one of them is about to give birth.