Property ownership

We can't definitively answer the question because it depends on too-many variables: you need to speak with an attorney about the specifics of your situation. Here are the possibilities, depending on the facts:
1) If you and your father own it as joint tenants with right of survivorship, or JTROS, then if he passes away, you instantly and automatically, as the surviving "joint tenant," become sole, 100% owner of the home. It never becomes part of your father's estate, so your stepmother never has the chance to inherit--it goes straightaway to you.
2) If you and he own the home as tenants in common (TiC), then you each have your own separate 50% interest in the home. In that case:
a) If he has a will leaving it to her, his share goes to her.
b) If he has a will leaving it to you, depending on how long they were married and the total value of his estate (what he leaves behind), she may still get part of, possibly even all, of his half interest in the house. That because Hawaii, like every other state with which I am familiar, makes it impossible to completely disinherit a spouse, so she is entitled to a minimum "elective share" of his estate. The calculation of what this would be depends on length of marriage and what is in the estate, but could possibly include some or all of his interest in the house.
c) If he has no will, then his estate passes by "intestate succession," which in your state means that she is entitled to the first $100,000 in value of his estate plus 1/2 of everything else (his children, however many there are, share the other 1/2 over $100,000) which again, depending on what he leaves behind, could include some or all of his interest in the house.