I do hope it continues to go ok.
As previous posters have said, it will be entirely up to whether your sister is ready to stop, down to her bones, knowing and understanding that she is an alcoholic and now won't be able to drink ever again. Until she understands this, she is still in denial 😔
Further to the excellent points Mrsterrypratchett has made about enabling.
Enabling isn't just buying drinks, or giving money, or giving them somewhere to drink. It's shielding someone from the consequences of their drinking.
By all accounts those poor children are at risk, living with two alcoholics, and their welfare is paramount. In any other circumstance, with someone other than your sister, I imagine you would already have raised a concern.
By not reporting, she avoids facing the consequences of her drinking.
Reporting to social services isn't a threat or a bargaining tool, it's a consequence. And it might help her in the long run.
It is also necessary for the welfare of the children.
I hope that makes sense, I don't feel I've explained very well.