It sounds like you might have been suffering depression when your DS got married. If your DS or DIL didn't realize how severely you were affected by the loss of your friend, they may not know how much of a break they should give you.
You are jumping to conclusions that you are not welcome to meet your GD. It must be hurtful that your DB is not welcome, but that is the prerogative of your DS and DIL. Your other brother should care for your DB to allow you to go visit. And tack a week on so you can take a much needed rest.
I don't know how your DS managed to travel 18 hrs for a farewell party, but it is nothing short of a miracle that he pulled it off. Leading up to a deployment there's a lot of paperwork, training, medical stuff, etc. The fact that he couldn't swing by and see you is not an insult, it's just a reality. In his shoes I'd be pretty ticked that I was about to leave for 6 mos, a year, whatever to a place where my life would be in jeopardy every moment of every day and my mother couldn't bother to come see me. It may have made him resentful not just of you but of his uncle. This could be why he's switched on being a caregiver for his uncle if needed. Also, he came back a changed man. No if, ands, or buts about that. You cannot deploy to a warzone (even if he was in one of the "safer" areas) and not be changed. He may be dealing with PTSD or any of a number of mental health issues. Don't be so quick to blame your DIL for any changes in attitude on your DS's part.
Your DIL sent you pictures. Don't try to read any ill intent in that. Don't be resentful that she didn't add a note. Be thankful for the pics and let it go.
Please, please, please get yourself some help. Get an outside, objective view of your DB. I'm sure you've had to deal with a lot of prejudice against him, but that can make you less likely to see his faults. He may be a bigger burden to others than you think. Or maybe not. Maybe DS and DIL are just being paranoid or prejudiced. You could be right on the money in your assessment. It's just important to keep in mind that you may not have all the facts or be the most objective.
Please get yourself some respite care. You need it and deserve it.