I’m so so sorry you’re going through this.
my mum died 27 years ago, my son was 22 months and I was expecting my second. My mum was my best friend, we knew she was going but she was only 59 and it was to soon and it broke my heart. I was there for my dad and for my brothers, for the first few weeks we held each together. Then my dad sort of drifted off, I thought he was becoming stronger but no, he had met someone, I was introduced to her when he came to meet his new grandson the day after he was born, it was the first any of us had heard he was in a relationship, 6 months after supposedly the love of his life died. Everything was about her and her amazing family, didn’t want any of us, we reminded him of mum. They married, we were told the day after, and told at the same time they were moving abroad. The family home had been sold and cleared, I asked about mums stuff and he was just noncommittal. They moved and we FaceTimed occasionally not often. Then my brother called to tell me he had heard dad was ill, and he needed us. We were to late. Stepmom called my brother and told him dad was gone, it was sudden, would contact us about funeral. I called her 2 days later and spoke to her son, dad’s funeral had been that morning. He had made a new will leaving everything to her. Yes we could have contested it, but what for. All our family treasures were gone, and it’s only money. I have wished for the last 11 years that she chokes on it but that doesn’t bring my mum back, or the man I thought was my dad.
if you’ve managed to slog through all that, what I’m trying to say is, let it go, it’s only stuff, your mums still with you and your children you don’t need stuff to change that. If your dad is in a relationship he will want to do something with your mums ashes, speak to him about that if it upsets you. But believe me, it’s just ashes , not your mum. I’m lucky, dad buried mums ashes and I have somewhere to go, but she’s not there. It’s took me a long time to realise I didn’t need her ashes or a grave or her things, she’s still with me I only have to look at my daughter ( a beautiful young lady who mum didn’t live to see and dad only ever met a handful of times)
just one last thing, the best advice given to me when mum died was from a very dear much older than me friend, she said “ loosing your mother is the worst pain, it never goes away, but it fades and you learn to live with it “