Estate Law, Dead Father, Disinheritance

LOCATION: Massachusetts

I am desperately seeking help with my father's estate. He just passed away 2 weeks ago and I can't afford a lawyer and just need some direction.

The problem is, my dad was suffering from dementia at the end. He somehow rewrote his will while in moderate -severe stages of dementia. He also apparently disinherited myself and my mother. I have been researching and found it's impossible to disinherited a spouse. And the only way to disinherit a child is to have a specific clause in the will that's says I am to get nothing.

He left behind my mother, to whom he was legally married to for 53 YEARS. They separated a long time ago, but remained close and married. I was adopted my them when I was 3 days old. They separated when I was 10 and since then he hasnt given a dime to my mother for child support, has done nothing for me.

My mom bought her own house, but her name is still on the deed of his house, where I grew up. He has made her pay for half the insurance and taxes for the last ~30 years while she hasn't lived there. So as I understand it, the house would be a joint asset, and therefore non-probatable. It's hers- separate from the estate right?

He apparently (I haven't seen the will yet) gave everything to his 2 sisters, who are moving as fast as they can to get items and get all the will dispersed. My mother is 80yo, still working as a CPA and has no time or energy to deal with this at the end of tax season. The house is worth over a million. He had over a million cash in the bank. A 100k+ car. etc,..

It's a rather large estate and I don't want to see my mother or myself get screwed. She's a CPA, and also helped him set up all his investment accounts that allowed him to die with all that money. He became very paranoid and angry and not like himself (though he was always an asshole).

Do I have a legal stake in his estate? Does my mother? Is it worth going to probate court? Does it cost money to consult with an estate lawyer? I appreciate any help I can get. Thank you!