After the death of their father 4 children must face their abusive mother and expose her lies and abuse if they want to have a chance at a happy life.

On the surface, the logline follows a clear structure, which makes it fairly easy to read.
You may find a way to avoid the repetition of abusive/abuse, and add a comma after 'father'. Because of the "and ... and", I would probably also put a comma after the second 'abuse'. That would make it a tad easier for me.

In terms of the story, I am not gripped by it because there is no clear point of view. "4 children" is too vague, as I don't have any particular character to engage with. At the very least, a logline needs to give us some detail about the main character, so we can get a feel for them.

Finally, "face their abusive mother and expose her lies" is not a cinematic goal. It lacks a definitive ending, so it is hard to visualise what the end of this movie could look like.
Great loglines allow us to visualise in our mind what the film would look and feel like.

I hope this all helps!