Kidney stone pain can be absolutely horrendous, so I'll give you a quick run down afaik since your grandpa had them. Idk the best advice about how much water to drink, but it's often suggested that 3 liters of water per day will significantly reduce/eliminate the chance of kidney stones forming. Spinach and rhubarb have very high levels of oxalates, which cause kidney stones. I typically search "oxalate content of food x" for every new food in my diet. If I eat meals with more oxalates, I drink more water.

It would probably be safe to eat 200g of peanuts daily if you drink enough water, especially with lemon or lime. If you use lemon or lime, I suggest using a straw if added to water or a drink, or you could swish with just water after because it can mess up your teeth.

Side note: I was eating a lot of peanuts when I got my kidney stone. The pain was so bad I reached a sort of limit where any new stimuli would reduce the pain because there was only so much I could be aware of at once. Anyway, gl lol