Op... I don't even know what to say that all sounds so overwhelming! That would drive me absolutely insane.
Your mum is being absolutely toxic. I'd tell her very directly that they need to step back to give you and dh a chance to adjust to being a family of 3, a chance to enjoy your baby and a chance to just get in the swing of things.
Your dsis, I mean she might have said things gently but has she had a baby? It's really hard on a relationship, my dh is brilliant and I love him and he's very hands on and supportive and I still wanted to murder him sometimes! You've still got all the hormones and sleep deprivation and the intensity to cope with- that doesn't come easy with any relationship. So that's normal! And given that your family are constantly around you're not really getting much chance to connect as a couple either.
You don't like upsetting people because you have been raised to believe that you are responsible for your parents emotions and happiness. Except they are adults. And you aren't. I was raised with the same expectation and I had a lot of hard fights to establish boundaries but we all get on much, much better for those boundaries.
I'd go back to your parents, tell them neither you or dh are happy with the constant visiting and calling but you do want them to be involved with your child so invite them for dinner one night a week and pick a set night. If that feels manageable to you. I set up a WhatsApp group and I send wee photos and videos on it so I don't need to do the constant facetimes. The other thing I'd recommend you do is busy yourself. They land round you say, sorry we're just on our way out. Sorry we've got this group, sorry I'm meeting a friend etc. We'll see you for dinner on our agreed night.
The hard part which is actually the key to it all is not caring. And recognising that as a new parent it is your right to establish boundaries for any visitors to your home. And if they don't like it, if they kick off, that's on them. I agree that your dh needs to step up and support you a bit here, I'd try to pass the buck on to him a bit- maybe he's having a stressful time at work and needs a quiet house with no visitors for a while ...?
Also just to say:
I gave DH a death stare and spoke to him harshly at a family dinner at ours a few weeks ago. It was because my family was helping clear up and he was just sitting there.
I would have too. That's rude.
My FIL lives in a 1 bed flat with his sibling who shares a room with him. The sibling is bedridden and so wears nappies. DH and I would prefer FIL to visit us instead of us take baby there.
Nothing wrong with that so would i. Easier to entertain baby with their things at home and you can look after fil making him tea etc and give him a break from his sibling.
Apparently I give DH the death stare a lot. And speak harshly to him a lot.
Welcome to new parenthood.
She said I am also irritable.
No wonder- you're getting no time to yourself, noone is respecting your boundaries so your needs aren't getting met while you're busy meeting everyone else's needs plus you've just had a baby and are probably not getting much sleep. What does she expect?