I would be wondering too!
You aren't entitled, blah blah, but it's fairly standard to inherit from one's parents (if there's anything left) so the thought will pop into people's heads.
One would hope that the remarrying parent would give some thought to what is fair for the kids of first marriage but in my experience they often don't and assume the new spouse will "do the right thing" when the time comes. This is especially true for men.
Your dad might have made provisions in his will for you or maybe not. If he does without a will his wife will get the first 375k (i think) of his estate, kids and wife get a split of anything left. But if their house is in joint names (joint tenants) she gets that automatically without it being included in the 375k.
If she outlives him she might leave her estate to you as she has no kids but no obligation to (and you'd probably have to wait an extra 20 years or so).
I note that she gave up working when she was 40. Was that when they married? If she has no income she may well need to spend whatever your dad leaves her so there might not be much left by the time she passes if she has a good long life, even if she does leave her estate to you.
My friends mum passed away last year and her will tied everything up nicely. She had been widowed and remarried but the house had been paid off by her and her first husband (father of kids). House stayed in her name and second husband got a life interest to live there but the legal title passed to the kids. Very sensible and well thought out. Second husband had his own kids and has provided an inheritance fund for them from the savings he made not having to pay a mortgage etc. She had been upfront about her will so everyone knew where they stood and could plan accordingly. I wish more people would!