Father left no will, how does the deed transfer to mom?

[Robert Cook]

Looking for some help.

My father passed away in 2007. He left no will and my mother's name was not on the deed, but she assumed the  loan on the house (she's been paying it for 9 years now). 

I understand in Massachusetts, since my father did not leave a will, half of the estate would go to his spouse (my mother) and the other half would be divided between the children (my siblings, all adults) . The house needs some work but she's unable to take out an equity loan to fix it up because her name is not on the deed. I am actually very interested in purchasing it from my mother but she is unable to sell it. Four out of the Five children (the 5th being my father's from a previous marriage) are willing to sign our shares of the house over to my mother if that's an option. My questions are,

Can the  4 out of 5 children somehow sign our shares over to my  mom? Will this allow her to sell the house and then just pay my half sister her portion and do we need my half sister's permission to sell at this point?

Can my other sisters and mother sign their shares over to me? And then could I just assume current mortgage? 

Can probate court be avoided? The house needs some major repairs that can't afford to be put off much longer!

Ive heard very mixed answers from several different attorneys and need some clarification.. I'd really like to take on this house and my mother does not want the headache any more. 

Thank you!!