Do you want your IL to be more of a part of your life? Do you want them to come and visit and stay with you more often? Do you want to call them more often? Would you like them to offer you advice and other things more often? Do you want to have to do the fakey smiley stuff more often, like your SIL has to?
If the answer is no--then I think that's where you start, as far as "feeling" better about the situation. There are often tradeoffs for a lot of IL attention.
I wish that my parents took a more active interest in my kids. I wish they would come and visit more often, not do short visits. I wish they bothered to find out what they were interested in. I wish they'd bother to get to know me. And then--I pull my head out of my posterior, because I remember that I really do not even want them in my business more than they attempt to be, I don't like accepting anything from them because of the strings, we have nothing in common and I find them to be annoying/out of touch/mildly horrifying if we spend too long together, ect. I'm sure they probably feel the same way about me. But all things considered, given the people we are--keeping things short and sweet and at arms length is probably healthiest and best for all involved. Oh, in my Little Miss Wants Everything Perfect way I "wish" things could be different, but they're the way they are, and I find it a lot easier to just accept and try to love my parents for who and where they are right now instead of walking around pissed that they don't meet my fantasy of what they "should" be.
Are you close to your parents/are they involved with your children? If so, why not focus on that? If not--are you sure you are not expressing anger at ILs for their lack of involvement/favortism because they're the safer emotional target for you? Do you have any older friends that might enjoy being honorary grandparents?
I think as they grow older you can have frank discussions with your kids, but also teach them to be compassionate. You can enlist (hopefully) other grandparents/grandparent stand ins. Maybe it would be helpful to work on establishing close contacts with your BIL/SIL/cousins that are independent of ILs, instead of allowing the ILs to drive a wedge between you--if you can build a closeness between your families, you may over time find out that you don't have much to be jealous over, since the ILs are a pain in the tush.
I also think that facebook is absolute evil when it comes to familial relationships if people take it as a measure of relationship/favor. I can't believe how not posting on a picture "as much" or a status "as much" can spiral way out of control with the drama! (I have seen this on friends and relatives FBs!) Uck. If you're going to get into a posting scorecard, then please be sure that YOU are liking/commenting on SIL's photos and statuses as much as you think other people should be commenting on yours! Not only will that pop your name/photos out at people more, but maybe you'll develop your own relationship with your SIL's family, esp. if she responds back! Keep in mind that most people do not scroll down very far--if they have 10 million FB friends who are posting about how their underwear is itchy or what kind of pizza they had multiple times a day, they may not have even seen your posts/pictures. I almost had to ban my mom from my FB because she freaked out at me that I was not posting "enough"--about HER!! Even though my last 5 statuses had been about what a nice visit we had/what we did--she just couldn't be bothered to scroll past all the Farmville/Bingo/Crap "updates"/other people's spam to see them. So...ugh. Take FB with a huge handful of grains of salt!!