Not inviting Embarassing family members to...

My sons 1st birthday is rapidly approacing. Recently some close non related considered family members have been embarrassing at any and all interactions. By this I mean the mother of 4 children is constantly talking about all her children ailments and then all their financial problems as well. At the birth of my son I was utterly horrified at the things she spoke about as I labored. My father in law was also present and she constantly talked about all the problems in their lives. Most of this is made up clearly munchausen and also by proxy both. Also she is a smoker as is her husband. It smells like her children and the parents never bathe. She also has meth looking mouth with teeth missing. They have been in our lives for nearly 13 year's. I am struggling as her children are jealous and try to take all the attention. I also have bipolar which makes these things high stress situations for me. I am having serious anxiety over having them at his party. I am attempting to limit interactions but it is proving difficult. What should I do? They will surely ruin his birthday for every one. Should i have a fake party with them and make it like a small party with few family members and then have a true party with all my real family and friends? I have no Facebook so they will not find out. Please help!!