I want to speak up to my 90 year old grandparents when they start discussing politics
Tell me why you want to speak up to your grandparents?
I cannot avoid their discussions as I am invited over for dinner and I want to say what I think.
It is good to participate in healthy discussions so you know everyone's point of view. Politics can be a nuanced topic.
I can't express myself to them in ways they can understand.
It takes time to get people to understand your point of view. Keep talking to them about how you see things and they will understand eventually.