OP, I am going against the grain here. I dont read your posts as entitled or selfish. I just hear sadness. I feel for you, I really do.
I could have written your posts when my dss were small. I was suffering from undiagnosed pnd. I did know that I needed medical help, but I also knew that antidepressants make you feel worse for 2 weeks before you feel better, and I knew that I wouldn't survive feeling worse, so I persevered. Going back to work saved my sanity.
I love my dss to bits, but having them for 12 hours a day until dh came home made me feel so lonely. I had moved home to be with dh just before I got pregnant so
I knew no-one, and babygroups didn't help much. I had no good friends and each day lasted an age.
What helped me apart from going back to work? MNet did - an hour or two a day of reading about/chatting to other mums who were, on the whole, very supportive. Sleep did. Mine were bad sleepers, but someone suggested going to bed when they did at 8pm once a week, so I booked a night off, not to be disturbed. The difference in how I felt was amazing.
Not expecting my relatives to be interested helped too. Like you I had been very close to my mum and she had been desperate to be a grandma. Then as soon as it happened she disengaged and was too tired to pay them much attention. '
Hang on in there, love. Things do get better once the babies are talking and can get out and about more. (Mine wouldn't settle or play indoors much, so we spent hours each day walking, puddle jumping, finding sticks, exploring. In bad weather having a list of activities to do helped. 30 minutes of this. Then tidy it away. 30 minutes of something different. And lots and lots of baths. Playing in the bath gives everyone a break. My boys had two or three baths a day in winter!
HTH. Hang on in there. Things will get better. And hopefully posters will come along with more positive advice for you soon too.