How do I know if I have to file an Informal or Formal probate for an estate?

My aunt recently passed away and did not have a Will. She had no husband, no children and both of her parents are deceased. She has 8 remaining siblings and they all agreed that the next oldest sibling will be in charge of the estate and become the Personal Representative. Her assets include approx. $10k in bank accounts, a home, in her name only, worth approx. $300k and a vehicle, in her name only, that is paid off. Can an Informal Probate be filed for her estate or does it have to be Formal Probate? This is in Massachusetts.