Grandparents harassing LO to eat

I know harassing is a strong word but I feel like it’s practically that now. They’re obsessed with trying to get him to eat and ‘finish his plate’. I’ve explained to them 100 times that he doesn’t need to finish his plate. If my son had a serious issue with eating then that’s a separate issue but he’s a toddler, sometimes they scoff everything, other times they nibble. He’s growing well and is otherwise happy day to day. If he’s having any meal at theirs, they will literally chase him around for 2 hours with a spoon, saying ‘eat’ ‘food’ or naming the food repeatedly when he’s trying to play with his toys and trying to shove the food in his mouth. Sometimes he’ll give in and open his mouth and they think it’s a victory but to me, it’s sad because he’s being taught to ignore his ‘full’ instinct. Which I don’t have, and now I know why. He’s 21 months so he can say no and I’ve taught him how to say he’s full so he capable of letting them know… which he does but they just ignore it. I kid you not, he could have eaten 4/5th of his food and they’ll harass him for a further hour trying to eat 2 more spoons. It gives me literally anxiety so I can only imagine what it feels like to him. It’s so bad, even snacks such as fruit they do it with. For example, they’ve peeled an orange and he only has 3. They’ll again chase him around telling him he has to finish the orange. I’m worried that they’re creating a negative association with food for him and it’s not okay. I just want to know if I’m being OTT in continuing to address this?