TBH, Newmum, I think you don't need to even make a decision to go LC or NC. Just stop contacting them yourselves and leave them to do it. See how long it takes!
I can see that it would be difficult for you, who seem to have a functional and close family background, to understand that other people don't always have that - but again, your DH does need to lead on this. Certainly you can have an input, and if your ILs DO contact you with regards to seeing you or their DGC, then (DH agreeing) you should probably see them, rather than refuse to respond. But. As I said before, if there is blatant favouritism going on, your DGC are likely to notice and be hurt by it, not now, but in the future. So be wary of letting that into their lives - a bad grandparent is often worse than no grandparent. :(
Your DH not wanting to talk may be down to him trying to talk to them before (as a child, a teen, a young adult) and them refusing to listen, so he's stopped bothering. You've already said they don't want to talk about it either, so it's a non-starter. You can't change this. Even if you got them together to talk about it, you can't make them.
Support your DH - but suggest that, rather than making an overt decision to go NC, you just stop contacting them yourselves and see what happens.