You and your husband don't have to accept mail, phone calls, etc from people you choose not to be in touch with. I like the suggestion to return the mail unopened. As for the visit, you don't have to visit with anyone you don't want to. Heck even if they show up at your door, you don't have to open it. And if hey won't leave you do have the option to call the police.
It must be hard to be in such a dysfunctional family. But you can set boundaries and decide what actions you and your husband will take if those boundaries are crossed.