Legal Question in Family Law in New Hampshire

Re: Which State favors me in divorce proceedings and custody?

I do not practice in NH, so my answer only applies to MA. The answer may depend more on individual judges than state laws, whichever state you go in. Your question is difficult to answer, since you leave out many facts. Neither state is likely to grant sole physical custody of a neonate or infant to a father, unless there is a serious problem with the mother that cannot be helped by a social service agency. How long were you married? Where were you married? Where were you living when the cause of the separation/divorce arose? How long have you been living in MA? Was there a custody or support proceeding in NH? How old are you and the mother? What income? How much time do you actually spend with the child, or does the child spend a lot of time with grandma and grandpa or an aunt?

Federal law discourages bringing custody cases in another state when there has been a proceeding started in another state, and state law follows the federal.

Since you were married at the time the newborn was had, there is a presumption that you are the father. You're right that siblings less than 2 years apart in age would be better off being raised together, but if they each spend more time with a different parent, I'm not sure that's much different from being born in a second marriage within the same period.

MA has a parenting manual which judges and parties can use to establish custody and visitation issues; you may want to get a copy online or at a probate court.

I am glad to see you are considering the children's and the second father's (if not you) interests. You really should consult an attorney at length, and you may be able to find one admitted in both MA and NH.