I feel so lost in my family since my grandma died
Why do you feel lost?
My mom forbade me to talk about it.
You cannot be expected to get along with your family all the time. You should be able to grieve the loss of your grandma the way you want and heal in your own time.
It's tough I have read a lot on this. Grief and loss might never be easier.
It's good that you recognize these facts about grief. It's never easy in the beginning but time heals all wounds.