My ex never remarried bu, infuriatingly, he did manage to emigrate to New Zealand a year before I did together with absenthusband. Jealousy was not the problem but there was a certain level of discomfort on my part as I always felt defensive whenever we met – both in England (we lived a few minutes' walk from each other) and here when he first moved to NZ and I was visiting nearly four years ago when my third grandson was born. I thought about this and decided it was my problem, not his, so the solution was mine to find. I addressed my "issues" and, after a few twitches, all is now well and perfectly friendly.
When the first grandchild was born (nearly 14 years ago), my ex issued a dictat that absenthusband could not, under any circumstances, be called grandad, grandpa, gramps or any other grandfatherly name. Rather than argue, absenthusband just stuck with his given name and now all is well and my husbands (don't you love it) are very amicable.
Where I am going is to suggest that you just think about the general scheme of things. The relationship your grandchildren have with other members of the family – blood relatives or otherwise – has nothing to do with how they feel about you and you feel about them. In the words of Nike – just do it. Good luck.