@Carolinejane: As you no doubt know, your dad is quite right that traditional proper manners call for the groom’s parents to call on the bride’s parents to initiate the acquaintanceship, with the formal reason that they are letting her parents know how happy they are to receive her into the family. But proper etiquette also requires that people who are better-bred, who perhaps hold to a higher standard of etiquette, must adapt to those who do not know better. Within the first few days of your future Mother-In-Law’s failure to make their acquaintance, a gracious alternative would have been for your parents to initiate contact themselves. Etiquette is just as firm that stubborn judgementalism is in bad form, as it is firm that the groom’s parents should have made the first move.
Now with her illness as an excuse for not taking the initiative — etiquette accepts that excuse, by the way — and with six months under the bridge, your parents have all the more reason to take the first steps, and simply invite you and your fiance and his parents over to tea or dinner. That can easily be done before “a few weeks” have passed and the chemo drugs destroy her taste and appetite.
The next planning step is for whomever will be the hostess at your reception — has your mother offered to give the reception? Or are you going to be the hostess there yourself? — to begin compiling the guest list. This is a second opportunity to engage your future mother in law. She should be invited to bring over her family address book, and you spend a happy couple of hours copying out the various full names and addresses, and making notes of how they are related, of all the people who have been significant in your fiance’s life to date. In the end, you may not invite everyone. But you get the full address list and relationships, so that later when you make the choice of inviting them or not you can actually follow through, and regardless so that you can send them Christmas Cards if you find yourself overflowing with Christmas cheer some year down the road. The hostess should propose this, and follow through on it, in a confident and secure manner. Show leadership, so that your future mother in law doesn’t have the opportunity to put a downer on things.
Your mother is also quite right, that your in-laws are not entitled to an opinion about the reception venue. But the reception hostess can certainly offer the privilege of consulting over such things, and for that manner over the catering and decorations too: it is the kind of feminine planning that some women love to share and compare. Such conversations are what friends are for. This has nothing to do with money, and everything to do with friendship. Which makes me wonder why, if she wanted to be engaged in this way, your mother-in-law has been so unfriendly to your parents.
What makes all the talk about etiquette and friendly consultation seem so strange, is the nasty money-talk. Whether it is “yes well she’s not paying is she” comments or “what a miser!” comments, they are rather vulgar, aren’t they? And your dad is, forgive me, a llittle silly to claim that “it is more traditional now to split things three ways.” It is more common, true, but “tradition” means “A long-established custom or belief that has been passed from generation to generation.” You can follow tradition, or you can adapt and choose a more modern praxis that is NOT tradition. What you cannot do, is pick a modern practise that works for you and then expect other people to make the same choice.
What etiquette actually says, is that no-one needs to pay for anything. Have the banns read, go to the parish church at the convenience of the vicar, have him consecrate the marriage with the verger and church secretary as witnesses, and you are done. Any social celebrating surrounding that act is an option of some lady who offers of her own free will to provide hospitality to guests in celebration of the marriage. Your mother has the right to offer first. If she doesn’t offer, your other kinswomen may offer — do you have a rich maiden auntie who loves playing hostess? Or you can play hostess yourself. Anyone who likes may support the hostess’s efforts financially, but polite well-bred people keep their financial transactions strictly private and out of the social domain.
You cannot force your dad to be gracious or your fiance’s mother to be friendly, and your dad cannot force anyone to split costs. You can only control yourself. I recommend you decide what kind of wedding you want that you can do without relying on others, and make it clear if they offer to get involved that you are accepting the offer ONLY on the condition that they stop behaving unkindly to one another and to you. And then (of course) be an absolute model of gracious behaviour yourself, so they have someone to imitate.