I understand OP. I was brought up by my DM - my father left home when I was 2, and I’ve never had any contact with his family. I believe he, his mother and 2 brothers are alive but I’ve not seen them since I was a toddler.
My DM is an only child, so I have no cousins, aunts or uncles. Her parents died before I was born, so no grandparents either. And I’m also an only child, so no siblings.
I now I have a lovely DH, and 2 DC (7 and 4). DH is one of four siblings, but they’re a very distant family and never talk. FIL is dead, we haven’t MIL seen for three years even though she only lives an hour away. She is not interested in spending any time with us - we have next to no contact (I got sick of her lack of interest and excuses, so stopped inviting her to things). My own DM is a doting and dedicated grandmother who loves our DC and we see her regularly (despite her living 2 hours away).
Thankfully, we are a very happy and self-contained little unit. We do everything together and the house always feels nicely full. On the plus side, my DC have a huge amount more family than I did but I do feel a bit sad that they don’t have cousins/aunts and uncles in their lives like their friends do, and they only have one grandparent that they see.