It sounds like the family are having a very hard time dealing with the privations of the pandemic lock down.
I also think that perhaps his parents are arguing for much the same reason, and he is acting out on you what he sees at home. We have seen a big rise in domestic violence.
If that is true, then the situation with all of you is a really serious one. Six year olds do not have the vocabulary to tell you just what is happening, and many children try to get help and communicate in the way your grandson is trying to either tell you about his situation or asking for your help.
There is always a reason why people do the things they do, especially in children who do not have the capacity to speak against their parents and other relatives, but they are canny enough to know when a situation is getting worse and they need to get help without raising angst against his parents. Only a professional can help you. Many people can see what is going on, but very few are trained to help you resolve it. In this lockdown situation, many trained counsellors are working online or by telephone, and many do not charge for the first consultation.
Your situation must surely not be isolated, so trained counsellors must have a lot of experience during this lock down, and you could try asking them.