The GP favouring their DD's kids isn't necessarily true Casper. My mum and dad favour my DB's DDs, yet I moved 350 miles away and back again to my home town, so that my parents didn't have to travel more than 10mins to see DD and DS. We are now less than 5mins walk away from my parent's house, and they're not prepared to call at mine yet are happy to spend 10 mins driving to my DB's house.
My nieces are treated better than my own DC OP and it hurts that my parents can fawn all over my brothers girls, yet we're ask to come over with our DC, then made to feel unwanted, as if they can't be bothered with the DC when we get there. Another example was Feb last year. We asked mum and dad to come over to ours for Xmas dinner, but they went on about how they weren't going to bother going to anyone's house at Xmas. This was way before we got the dogs. Lets just say that I was pretty angry when I found out that mum and dad were going to golden boy brother's house.
In contrast, my IL's were the ones who, in my mind, replaced my parents as they were the most loving, respectful and fun people you could meet. They absolutely doted on DS. They were the parent's I should have had, not the parent's I got, but unfortunately there's nothing you can do about it.
It's hard when you feel like your family don't matter to your parents or IL's. My advice is to just move on and live your own life. Some parents like to be needed, and to be totally independent from then tends to make them feel like they're being chucked on the scrapheap. Anyway, if they don't want to make the effort to see their DGC, then that's their loss. I don't ask my parents for anything now and as far as I'm concerned it takes 2 people to put in 50/50 of effort to keep a relationship going. If the percentage is higher, without acceptance from the party doing the majority of work, then resentment will build.