No I've know them for three years prior to us getting together
No I've know them for three years prior to us getting together
It doesn't actually matter how long you've known them for. It doesn't matter if you are the greatest stepfather in the world. It doesn't matter if you poured your heart and soul and raise them up as your own. It doesn't matter if you support them financially 100% because the dad is a deadbeat as you claim. Your two options are you have the mom try to get a court order to change the names and watch it get dismissed in court if the father objects or wait until the children are old enough (I believe 18) and they can as adults change their last name should they wish, if you are still around in their lives by then, and if they actually feel like they want to by that point.
If your spouse uses a name for the kids other than their legal name, she will encounter limits -- it is unlikely that the school will allow enrollment except under the children's legal name, or that they would be able to get ID under anything but their legal name.
Any legal name change must be made by a court, and the father is entitled to notice of any name change petition. If the father objects to a name change, the court will require proof that the name change is in the best interest of the children. Contrary to what is suggested above, the mother will not automatically lose if the father objects.
I know of a current situation where the gal who is involved has made note of the practice and commented that it should not be practiced. The judge is free to use the recommendation or not obviously . While it was not the biggest problem in the overall situation, it was mentioned by the judge that the children should not be calling a stepparent mom or dad.
I suspect the mom or dad did express their dislike for the practice but can't say with any certainty.