You Probably Can't

First be firm but do it with love.  Address the reasons why if you think that might help. For example I try to make it  point not to call a friend when I'm angry because once I start to tell a friend why I feel angry I get daihrea of the mouth. So I try to work off anger instead a brisk walk or go into the woods and talk to yourself and then address the person you are angry with.

My son was considering dating a girl who had hired him to help clean the garage at her home but decided not to. One day when she nailed me on the phone i knew why. End of story.

Then there are people you just know you don't want to associate with.

The users: I just tell them I don't like one way streets. They  always call you to help them and when your need help their too busy.

People who talk to their children with foul language and complete lack of respect. People you are adicted to alcolhol . You can try to allow them to visit your home sober (turn them away if they are) They are not allowed to turn your non alcoholic party into their kind of party (especially a childrens party)

So the rules are they come sober, do not bring it with them and leave sober.

It they can't do that  they won't want to come.

My son had a "friend" who wanted to celebrate my son's first year of sobriety with a keg party.

Then there are some you can't be nice to but divorce yourself from them completely. For these I saw a T shirt in a mail order catalogue. It said Support Search and rescue Get Lost.  I wanted it to wear for the ones you divorce yourself from but they are usually at your grandchildren's birthday parties, But they would not get it. Which means it wouldn't be worth the cost of the shirt. Because people have to be pretty bad for me to feel that way about them. 

I wish you the best but please keep in mind you have a perfect right to divorce yourself from anyone who is that unpleasent ,or dishonest,obnoxcious even if they are related. If you and your husband have relatives that anoy you that much is  is alright to divorce your selves from them.  I have people  I know who come from dysfunctional families and are very well adjusted considering their background but the most dysfunctional members of the family draw them in for another favor they get upset and show the dysfunctionality for days afterward.