What to Do For The Best??

She was very young then when she had her two babies.
It sounds as though she is having her ‘teenage fun’ a little late as she is a mother to 2 small boys now.

Somewhat irresponsibly - what happened about contraception?

Does she want this baby or is she considering a termination?

I am 46

She is 22 now

Sadly sometimes Nanamilly there is nothing we can do. Our adult children choose their own path and need to learn from their own experiences. Unfortunately in this case it involves not just your daughter but her children as well.
I would not help her as much as you have been doing, support the children but let her find out her actions have unpleasant consequences. Tough love sometimes needed and its hard to see your child behave like this.

some people have a brain condition, whereby they cannot assess risk well, look to the future, resist impulsiveness, or make sound judgments, to the average ability.
any sign of this when growing up.
anyway, it doesn't really help unless she sees she has a problem and seeks help for it.
how about the children, are they being well looked after, what stability is she able to give them.
could she be persuaded to seek help, psychological help, for their sake, or homestart for practical help and support.
I know you do that, but maybe an outsider being neutral, might have more traction.
can see it's a great worry. hope you all do ok.

I don't see there is anything you can do. They live their lives the way they want to. Just be there for the boys. Let her get on with it.

Enjoy the new baby when it comes. Hope you are not too old.

How old is she now?