How often can I attempt to contact my grandmother before her live-in son can legitimately report it as harassment?

I was speaking with my grandmother when her son(my uncle) started yelling and cursing in the background(my grandmother and I were discussing my children). My grandmother apologized and quickly hung up the phone. Her son has lived with her rent-free for 2 years and is unemployed. I was then unable to contact her for two days and contacted APS to do a welfare check(Although he made no threats, he was extremely vulgar and vicious). Their report did not find any abuse that they were able to tell me about. That was a week or two ago and I am still unable to reach her by phone(she had always picked up or called back before). I went over to check on her myself with my spouse and 2 children, but he was cursed and screamed and told us we were trespassing. My grandma could be seen across the house on the couch, and when I asked "are you ok?" She nodded despite being in tears. A week or so later, the son picked up the phone when I tried to call and told me that if I keep trying, he will file a harassment charge. I care deeply about my grandmother's well being and her relationships with my mother and my children, but do not want to be in trouble with the law because I am harassing the son by calling. How do contact my grandma and continue a relationship without harassing the live-in-son?