She brought it up before anyone else.
Secondly, you and I both know that you cannot change anyone else. You can only change yourself. I looked and know I posted one sentence stating that or paraphrasing it.
Others seem to think it doesn't matter if(as long as) they love each other. How many marriages have you and I seen fail because love was not enough? How many times have folks with the best marriages shown respect, lovingkindness, and a compatibility that includes and goes way beyond sex?
The easiest thing to do is to find another man, someone who is more compatible in all ways.
Next, be gracious, kind and humble in the face of the adversity.
Next, hope that he loves you more than his children, so that he will defend you enough to satisfy your desires to be respected as a motherly figure in their lives.
In truth, it is easier to prove to them through actions with them that you are worthy of their respect and love as a motherly figure in their lives. That's truly damn tough to do when they are with their mother and father more than you.
Ex.: Helping them in the face of adversity, as in, saving their lives when they are drowning, as an example. Please do not create the adversity to achieve your goals. Your plan and actions would be discovered and found vicious and sick, if not illegal. I do not believe you are that type of woman. I felt a disclaimer was necessary.
One thing that might help is learning about how to handle parental alienation. That's basically what you are and will continue to go through. As I said before, good luck, or whatever positive terminology means I hope you get the respect and love you deserve, though I know there is so much against it, along with changing your life through marriage.