What exempts a Catholic from going to Mass on Sunday at church?

My grandparents are devout Catholics in the Midwest. They are fairly involved in their local church, however if they are away they will go to any close church. This much is fine, and I admire them for their faith and dedication. As they were born and raised in small Midwest towns during the 1940s, I believe that their dedication to this has to do with their interpretation of "remember the sabbath day" to mean that they need a church and priest. Where I have concerns is that, last Sunday, the roads were icy enough that they were having trouble safely driving and walking. This is boosted by both of them reaching critical memory issues, and my grandmother not eating enough and relying on a walker. As such, I am concerned for their safety, and want to give them an alternative if the roads are too dangerous for them. Since they are devout, I am looking for something in Catholic doctrine that defines whether or not a priest or physical church is necessary for worship. A preferred or additional verse would include some prioritization of your own health. EDIT: Thank you for the answers! I didn't realize that Mass was a compulsory idea since I come from a Protestant background. I'll see if my grandparent's friends aren't willing to pick them up. God Bless!