D.W.
O.K.... what time do they plan to arrive? (Wouldn't it be great just to leave a half hour before they come and leave a note on the door explaining that you had other plans -- lol).
O.K., now for the reality... go to the $1 store and buy some Halloween dish towels. Hang them on every cupboard door. Set the table with everyone's name at the plate. Do you have a breakfast bar that's next to your table? Maybe the kids could sit there so they are closer to the table and feel included too? Then, have your husband or kids answer the door. You stay in the kitchen! Have treats out on the counter, and hot chocolate and/or apple cider hot on the stove. Tell everyone to help themselves and to find their seat. (You are in charge now). Tell your husband that he's not allowed to leave your side the whole night or you will refuse to have them over ever again! Or just simply state to your FIL that you appreciate his comments, but this is your house and your rules.
Do you put your 3 year old in a stroller or a wagon? (It makes it more fun for her and doesn't wear out her feet too). Have it all ready to go with a warm blanket and your coats. Tell everyone it's time to go and that you'll be in front and that they can follow. If you don't want your MIL to hand out candy, don't buy candy. Simply tell her, if she asks, that you didn't buy any this year because you didn't think anyone would be home to hand it out (or if you want to be a bit meaner: say that she should have bought some if she wanted to hand some out).
Best wishes to you! Try to have fun!! Make up your mind to do so, and have the action plan in place.