Can my mother sell her home to me without my stepfather involved? She owned this home long before the marriage.

Sdad is on the deed. Thats a problem. But Mom owns half the house. It's no different if they bought a house together. It's her home, her rules. And I would hope if StepDad could there he would be standing behind ur Mom.

How long has stepdaughter been there and why? Has she paid rent? Utilities? I think getting SD evicted would be ur best bet. SDad owning half the house does not mean she has a right to live there and make Mom uncomfortable in her own home. SD is now an adult and needs to be on her own.

You would only be buying half the house unless stepdad is able to agree to the sale. Is he competent, if not does Mom have POA? Does the POA read she can sell as his rep if he is incompetent?

You may need a lawyer to sort this all out.

It depends entirely on how title is vested, i.e., in whose name the deed vests title.

If she inherited as the sole heir after his death, then she can sell it.   Check the deed; how is title vested (described)?

As to someone smoking in a house with oxygen, that's not only a big no-no, it's a recipe for disaster.   Do these stepchildren live with your mother?  If not, she has the right to ban them, especially if one refuses to stop smoking, which is not only dangerous but negatively impacts your mother's breathing ability. 

In addition, someone who screams at an older person is not a desirable person to have in the house.   Maybe she needs anger management counseling.

Your mother can evict this person but will probably have to go through legal proceedings to do so.    Still, it can be done, and from what you write, SHOULD be done, ASAP, to protect your mother's health.

In most states, inherited property is separate property, so assuming she kept titled in her name, yes your mom can sell.  But I would get an attorney involved.   I am guessing this rotten stepdaughter thinks the house is her dads.