I am glad your dad is fine with sexuality.
My thoughts on your mum reaction. I think your mum needs time to get her head around this change in her life. As children are a big part of a parents life, even if they don't admit it.
It sound just like When a friend of mine Clare came out.
Her mum looked shocked and headed off into the kitchen to bake. Clare called me saying that she came out, and explained her mums reaction. So I popped around as Sarah (her mum) liked me and would always chat with me.
I walked into the kitchen and after a awkward silence Sarah spoke "well that Bleep me having grand kids, I thought you and Clare would get together and you know, umm, have a family. but this has Bleep it". After we had a chat where i joked about a item Sarah had in her Christmas dinner equipment draw, she laughed and admitted the future she saw that morning was very different to the one she saw that afternoon.
She loves Clare's girlfriend Deb and is now bugging them for 2 grand kids, one from each. and has commented to me and my wife a couple of times that i should give them a hand.
Her plan for grand kids did not die, it just ended up looking for a different way to get them