I can understand why you feel hurt at the fact that there are photos of your DiL's parents in the house, but none of you, as you probably feel that this is a bit of slight on you.
My son and DiL do have the odd photo of us, and DiL's parents in their home. Although, generally, DiL takes lots of photos of GC with her parents when they visit, but rarely takes photos with us, and my son isn't one who bothers to take photos unless I ask him! Usually, it's down to myself and my husband to take our own photos with our GC when we visit, so that we have lots of memories, and there will be plenty of photos of us with our GC if they want any memories of us in years to come.
Personally, I've never had photos around the house of my own parents, or my in-laws, so I wouldn't automatically expect my son and his wife to have any of us.
As long distance grandparents ourselves, I think the best suggestions for your GC to remember you, and to engage with you, is to skype/facetime regularly ... although, don't be offended if all you get is a 2 second smile and a wave, as they really do have more interesting things to be doing, rather than talking their GPs! Sending the odd little gift/toy/book, along with a message/photo in a card, will no doubt earn you a few points too. And whenever you do get chance to visit, shower them with love, and fun times. As they get older, they will no doubt look forward to your visits with excitement.
I don't know what your issues are with your DiL, or why you don't get along, but for sake of your relationship with your grandchildren, I'd suggest you bit your tongue, put a smile on your face, and try your hardest to be pleasant to her. It's a small price to pay ...