You are in a hard spot because you know that it won't be met well by her. Even if you see and feel that her way is the wrong way, I would try and not focus on that with her. I would simply let her know what you desire to have with her kids and that is a close and loving relationship that aunts and their nieces and nephews love to enjoy. Let her know you love her and respect her as the parent and hope that she can see how wonderful this relationship between you and her kids is and that she can allow you to cultivate more time with them in whatever way works for all of you.
While you won't be able to change her and her vies, it is possible if you speak to her from a place of love and desire that she might be able to hear you and allow these relationships to flourish.
Not easy, I know. I wish you the best...try not to use the words jealous and possessive...they can be lightning rods. Go easy and speak from the heart and what you desire.
Let me know if I can support you further. If all good for now please take a moment to click the rating tab to rate my support. Thanks so much in advance. Wishing you a very Happy Birthday on the 11th.