What do we need to do to put the family home in my sister’s name after mom passed away?

Somebody files a petition for probate. Four of you file assignments of your interests in the estate to Sister. The four of you also file gift tax returns.

If title is in Mom's name alone, probate will be necessary to pass title. Please see a probate lawyer.

For title to the property to pass, the house must be probated. The live-in-boyfriend has no legal right to the house or any part [unless he can convince a judge that he put money into the house or paid some of its expenses so is entitled to get back his contribution, but that is a weak argument as often even a spouse can not successfully make it, but you should check with a local probate attorney]. The four children could then all decline to take any share and quit claim their interests to the one sister [or them could take their interest and then quit claim it, but there is no advantage to doing it that way; there is no inheritance tax on the amount taken by an heir and none on the estate if it is below a certain fairly high amount it varies depending on the year of her death. It probably is best to see a local probate attorney and see what is the best way to go. Most will not charge for a 15-20 minute discussion.

With no will or other estate planning instrument, the property will have to be probated to get the title into the sister's name. You should consult a probate attorney for assistance with the process.

Contact a probate attorney to file a petition in probate court, to probate the estate of your mom; during the course of the proceeding you and your siblings can decline your respective share in the estate in favor of the sister who took care of your mom at the end of the probate proceeding this will allow the court to order the title to the house to be put into your sister's name.