My dear...get it all out! Go and punch pillow!! It looks like you've had it up 'here' (hand on top of head) with H's shenanigans. I do FEEL for you here.
You can tell S18 that any phone calls with L is your business and only yours. Not to be shared with other people. It is an adult thing and not for S to know.
You can instruct your L that there's an open visitation for H to visit your boys at any time. They work FOR YOU. Be sure that part is clear to L. And she can have it in writing for you to review.
