I'm so sorry you've had to suffer from your family's willful ignorance. Hopefully your wife, MIL, and FIL make it through all right. I can definitely appreciate your anger since I went through it a month ago.
While both of my parents have taken COVID seriously, Trumper family members have not. Just before Thanksgiving, my dad had to go to help my grandfather with something at his house. Two days later, he fell ill and tested positive the day after Thanksgiving. He ended up infecting my dad, who infected my mom. Fortunately, they all had very mild cases.
I have an aunt, who "God told me Trump was still going to win," that refuses to wear a mask despite being immune-compromised after a kidney transplant. It took her doctor explaining 20% of transplant patients who got COVID died to get her to commit to getting the vaccine. At Thanksgiving, my mom felt like our family had to attend to ensure it stayed outside since the rest of the family would've had it indoors as if nothing was going on.
The hospital in my hometown is now opening up the administrative floor to use for patient care because it is being overrun with COVID patients because of people like this.