Shelbel The acceptance of there being no chance of resolution with your father is very hard. And you know you face the same with your Mother, making it even harder. There is no one answer right for all whilst going through this but do be kind and understanding to yourself You are grieving for what you didn't have, for what you hoped you would have, for that small hope of resolution with your father that will now never be.
Don't question yourself over the card. You sent it, what your mother thinks/makes of that is for her to deal with you. Try not to focus on your sisters not doing what they said they would. Try to focus on yourself, your needs and moving forward without and despite of people who have caused you harm.
For some, thinking about small glimmers of "good bits" can help, for others who have suffered an awful lot of "bad bits" it doesn't help at all, especially if bad always followed any "good"! Just do what you need to do and look after yourself 