Is marriage legal ?

Yes. It is still legal. You can get it fixed.

Joint custody/child support issues

You need to enforce on the custody side with an attorney and make mitigate any possible upward change on the support side.

Can my boyfriend grant me legal guardianship over his daughter without his parental rights being affected ?

Something does not sound kosher here. Who is terminating the mother’s rights? What do you mean in the middle?

No. You cannot do that. It would not be valid.

Can a father register his son in another state when grandmother has residential custody?

Registering him another state as what and for what??

Mother absent for 7 months

File for sole legal custody. ASAP.

What are my rights and how can I remove/evict a live-in nanny (with a child) from my home?

You have a real issue on your hands. First there are labor law issues. Second you need to start eviction proceedings to get her out. Speak to an...

Going through a divorce. Ex filed in May, served me in July. There is one child born January 2017 whom I financially support

If the child lived with her primarily then she will be able to claim the child even if you paid support.

Depending on the act committed the 15 year old may be charged as an adult or most likely will be tried in family court.

Is there any legal problem giving my boyfriend's last name to a baby legally even if he is still married to some one ?

You can give your baby the last name that you choose. Will he sign the acknowledgment of paternity at the hospital? There is no legal issue for him...