OP,
You don't think your husband understands......oh he understands.....he understands perfectly well.
That is why he takes his lunch time when he does, skips to the garden when he does, and basically does the absolute least he can get away with.
A two year old, and a new born, is relentless.
He knows only too well that you are struggling, but he would rather chance that his post partum wife have a nervous breakdown, in the bombsite of a house that you live in.
Anything, rather than step up and behave live a decent partner and father.
You are married to a right selfish prick.
Make no mistake about that OP.
A right selfish prick.
Good men, do NOT behave like this.
Take a good hard look at your situation.
You need to protect yourself and your health.
Because you are married to someone who is fully prepared to really roll the dice with your mental health.
Contact your parents and let them know.
Reach out to friends for support IRL.
They need to know exactly what a waste of space you are with, so they can support you.
Finally, this is NOT down to you.
You sound like a very strong woman, whom has been putting up with too much bullshit from her husband.
He needs to step up.
Because believe me, you will NOT forget this time, and how utterly selfish he was, and it will poison your marriage.