@ZanySheep youve misunderstood what was said. No one is saying you're a gold digger, but you need to consider that if you marry your OH, then your assets could be at risk in terms of your DC receiving whatever you want them to inherit, unless you make provision for them. This is in the case of you predeceasing your OH/DH.
Take it step by step. OHs divorce has to be finalised, nothing can move forward for you until that happens.
once the divorce is finalised, you need an honest conversation about wills, ensuring that even if you get married you both agree that your respective wills need to reflect your individual wishes for the assets you're both bringing into your marriage to go to your respective DC in the way you each choose. If you fail to address that, you're both setting yourselves up for a world of heartache later on. So many people fail to address this properly, they don't think about the implications for their children. You have the opportunity to do this at the right time, before you get married, so it's clear and agreed.
whether or not you have or have not met your OHs offspring is out of your hands. You have no control over the circumstances, nor what your OHs ex wife has discussed with them.
The fact you have never met them speaks to a very fractious and negative situation surrounding the break up of their parents marriage, you may or may not enjoy a warm, friendly relationship with them if their mother has influenced their perception so significantly (parental alienation could be at play). Is that something that will eat away at you and taint your relationship with your OH/DH or can you make peace with that situation? will it make future family gatherings impossible or unbearable and uncomfortable for you and your children? Only you can decide that.