One thing I noticed in reading this is it not only seems your anniversary is ignored, but I see no mention of anything for your Mom. I did notice she and your father are no longer together, but is she remarried? If so, I have to wonder why no party for her either? (Just my observation)
I get the idea you would enjoy your aunt's parties thoroughly if you weren't feeling sad about the way your anniversary is neglected. And that seems like a pretty normal reaction.
Do you have any idea why your aunt's anniversary has become such a big deal every year? I can see celebrating as a family on the big anniversaries, but most couples I know prefer to do something as a couple other years, and family members simply send a card or possibly a small gift, and leave it at that.
My recommendation is since you are feeling resentful, you simply tell your mother that you are not going to be able to participate in the dinner, but will send a card to acknowledge the anniversary (if you decide to include a gift, just do it, but don't even mention that to your mom.) In seven years when it is their 50th, participate in the big Golden Anniversary celebration, but just be sure you have "another commitment" on the other years. Then you and your husband go out and have a nice time together on your anniversary. If you choose to do something that includes your children, that would be great. If not, why not ask your mother to watch the children for you while you go out? That would be a nice, subtle way to remind her that you have a special celebration time too. Even if she won't take the children, or even if you'd rather not leave them with her for some reason, just the asking would be a reminder.