What do you do when you want a relationship with your siblings, but they don't seem to want one with you?

I have made it known how I feel.
I have asked why we don't get together and do things.
(I got no response, just "I don't know, we don't know")

This has been going on for years,

We have never been close.

We are several years apart, but since we are all adults, that really shouldn't matter.

Mom mentioned getting her grandkids (my nieces) Valentine's gifts.

I stated, " I would get them something but I never see them"
(Custody battle issues).

Then mom says, you should come on Saturdays, they come by almost every week.
(As far as I knew, they were with their dad every weekend)

I haven't seen them in months, yet they congregate 10 minutes away nearly every week and don't bother to mention it?

I really wonder what my future/ family/ holidays will look like in the future.

It's hurtful

I'm torn between saying something about it for the last time, even though I shouldn't have to, or just moving on and not talking to them anymore.