Okay, it definitely sounds like you are overwhelmed at the moment. It’s completely understandable, given what is going on. It doesn’t sound like PPD, though. To me, at least.
I have a 9 month old, and I get overwhelmed at times, and I don’t have half of what you have going on. You really do have my sympathy.
My only real advice is to perserve getting your baby onto a bottle, so that someone else can take over feeding (EBM or formula). I had exactly the same problem; a baby that would only take the breast, and refused any bottle with screaming and crying. It was heartbreaking to hear, and kept me tied to the baby all day and night. Sometimes this just isn’t good for your mental health, no matter how much people tell you it should be the most rewarding thing ever.
I tried all the usual tricks - different bottles, and other people trying to give it to him. Nothing worked. What did eventually work, was finding the right bottle (My First Years Breastflow - I have no idea if you can get this as I’m in the UK, but it has an inner and outer teat that mimics BFing) and ME giving it to him. I would start feeding him as usual, and when he had had a reasonable amount, I would slip the bottle in, in the same position that he would normally feed. And he would take it!
It did take a few weeks before anyone other than me could give it to him, but we started with my husband giving him a bottle at his dreamfeed at 10.30. He was too tired to really notice what was going on. We built it up so that eventually anyone could give him a bottle.
It gave me some freedom back, and some sanity. But it took trying something that was the opposite of what everyone else advised (ie me doing it rather than get someone else to try the bottle).
I have no idea how to deal with the MIL issue (or rather your husband’s response to the MIL issue), but I do feel that if you could just get a reasonable break from the baby, you’d feel so much differently about things. It really helped me to know that the baby wouldn’t die if I couldn’t make it back in time!
Please go easy on yourself. You’re dealing with a shitload at the moment. A new baby is hard enough without everything else.