I have ten year old twins. And they are just incredibly awesome.
But the early years are hard. Really really hard.
You aren’t failing.
You might be expecting a little bit too much of yourself though.
My rule was that I did whatever I needed to keep myself sane. The babies needed looked after, I needed to be looked after where possible and everything else could go to hell.
So I took them out for a walk in the fresh air every day. I walked miles and it really helped.
I tried to make sure I had an adult conversation everyday with someone other than my DH. It might be going to a baby group, it might be going to the story time at the library, it might be inviting friends round, it might be chatting to an old lady in the high street.
The house was kept minimally clean and my DH did much of that.
Time just with your partner is important too. I breastfed mine so it was hard to go out but we used to put them down after their 8pm fed and sneak out the house keeping our fingers crossed that they wouldn’t wake up and scream at Granny. 
I found finding time to eat hard so DH made me porridge before he left for work and left me a sandwich in the fridge for lunch.
It will get easier. I found 12 months, 18 months and 2years big watershed moments.
A PP is right 3 years was a key age, no more nappies, no more high chairs, no more pram and they can talk!
I remember when they were toddlers a friend with a singleton the same age saying how she missed the baby stage. I was completely agog! The baby stage with twins is so hard that everything afterwards is always easier.
Hang on in there. It gets easier. Honestly. And talk to your twins club people, I bet they understand exactly how you feel.