I think you’re very wise to understand the connection between the loss of your grandparents and the fear you have with your mom. Your heightened sensitivity makes a great deal of sense.
Are there other family members, or extended family members you can talk to about this? Perhaps an aunt or uncle? Talking to another adult about these feelings may be helpful as they will be familiar with the situation — and could possibly offer you some ways to cope.
If family members aren’t available locally — try calling via Skype. If a family member isn’t available you may want to try talking to someone at your school or place of worship. The kind of grief and anxiety you are feeling is very understandable. Finding someone you trust to talk to should be helpful.