Lucky, I'm really sorry.
My advice is, if you love your Dad and want to connect with him, do what you can to be there for him and communicate that love to him directly.
NOT through your mother, or messages, etc.
If you're at a distance, you can still find creative ways to send those direct messages. (At times I would order something for my Dad with my own message/note/gift...so there was no way for my mother to hijack my communication and make it about her.)
When you're focused on your own feelings of love and grief, and being present to him and to yourself...if you can possibly look at her the way you would annoying weather, but keep your eyes on the prize (being present to yourself, and to him)...that may help.
She IS just annoying weather. Way more sound and wind than substance, and fated to blow over.
You're sturdy. She cannot blow you over. Love is bigger than fear.
Just love yourself, love your father if you do...and respond out of that place.
(Loving yourself means not letting your mother make it All About Her.) You can be compassionate
but protect yourself at the same time.
love to you,
Hops