What to so when my husband ex wife is always messaging my now in laws?

[Barb Outhere]

"What can I do to win them over as much as she did?"
Firstly, do NOTHING to interfere with her relationship with them. That will only lead to resentment.
Second, be yourself. You should not trying to "take" her niche in their lives, but work on creating a special one that is just your own. Treat it like a competition for their affection, and you will seem mean spirited.
Third, work on making your relationship with your husband a good, healthy and happy one. The parents will appreciate the fact that you DO make their son happy.
Fourthly remember that you, as an individual, have just as much worth as she. Do not allow the thought of being second to enter your head.
Hope that helps.