I think it was brave and courageous of you to go to your uncle's funeral, considering that it would mean exposing yourself to unkind people, pain, deceit, lies. But I think you did the right thing for you, to honor your uncle who was actually one of the decent people in your life, it sounds like. It was for him and for you, and to hell with the others and their lies! I get why your MIL might say what she said, but she doesn't really get why it was important for you to go, even though it did mean exposing yourself to pain.
And the whole thing about your dad and the smoking and the cigarettes .... I don't know what all words I'd want to use to describe my initial reaction to reading that, but it would be something like this ....
What terrible, stupid attitudes and actions. Of course it would hurt you badly. I'm sorry you had to endure that. I can see myself doing the same thing, meltdown city!! But it was probably actually good for you. So what about using the F word in a Catholic cemetery; I think the good lord is probably much more appalled with the attitudes/actions of those putting cigarettes on the grave than he is by your F word and pain and reaction.
Your kids ARE special.