I might go off in some tangents, so I apologize, and please bear with me. It seems as if you may have some issues with your father, whether he's overprotective or super strict, I cant' tell - so I can't really give you anything there. BUT - I can clue you in with divorced parents. If you are going to have any sort of wedding/ reception with people - hold only one. It is not your responsibility to accommodate a couple who couldn't keep their promise to one another, and now can't stand the site of each other. How do you do birthday parties for you child? Do you hold 2? It will take a lot of bravery on your part, (I had to do this too), but after you tell everyone however you tell them, get your parents, step parents, step siblings together in one place and tell them that this is your wedding. You will not tolerate any bad mouthing, jabs in the back, back talking, etc... from any of them from now through the wedding, or they will not be invited. No warnings, they are adults, they need to watch their tongues. This wedding is not about them, and if they love you, they will step up and try to get along. Put it on them saying something like "If any of you feel that you are not able to keep this promise to me, then tell me now and we will discuss nothing of this wedding until it is over with you Because I will not have negativity around us during this happy time, nor will I be surrounded by fear that none of you will keep your promises" You can not please everyone, nor do you have to try. Put it on them to prove to you that they can be responsible adults, acting in a responsible manner or they can't come to the wedding.
If your fiance's family lives really (!) far away, and can not afford to travel, them maybe do 2 parties, but if they can travel, think about holding only 1. There may be less of a turnout, but it will save you money.
Both me and my husband have divorced parents, and we had to do this too, because neither set really wanted be around the other. That set the stage for parties, knowing that we will only hold one birhtday party for future children, for ourselves, if we hosted holidays, etc... Now 10 years later, we know that if a parent doesn't feel comfortable, it's upon them to leave, not us to appease them.
Good luck!