For some reason it seems easier to write this one third party, I hope this makes sense!!
[background] The Smiths and the Jones live in the same city, but opposite ends - say a 30 minute drive in between. They don't really know each other well, but have mutual relatives (something like Mrs Smith's brother married Mr Jones' aunt). Let's call the resulting family the Browns. The Browns all live in thousands of miles away and have never lived in this particular city. When members of the Brown family come to or pass through xCity they are welcomed with open arms by either the Smiths or the Jones family, both of whom LOVE to host (and would be very surprised if the Browns stayed in hotels instead of asking for a bed for the night!). Depending on who it is, their reasons for visiting xCity, or possibly time constraints they may see only the family they're staying with and not visit the other. Other times they might stay at one but visit the other. [end background]
Occasionally a rare situation arises where the entire Brown family have reason to visit xCity. In those situations, there might be some people staying with the Smiths and some with the Jones - note that this is not a coordinated system, and it's really just based on who decides they want to stay where and makes arrangements. Coming up soon one of the adult children of the Brown family has a graduation ceremony in xCity, and the rest of the family have decided to attend. Several members of the Brown family, including the patriarch, have arranged to stay with the Smiths who are now "fullhouse". This leaves the actual graduate and their family the option to stay with the Jones. There are no formal events arranged around the graduation e.g. dinner, party etc. The Smiths are apparently
intending to entertain the whole Brown family at their home to celebrate the occasion. However, as this is an occasion that impacts the wider family, it seems odd to have it hosted by one of the households unless there is some kind of arrangement in advance to include the other. Also, the graduate has some other friends they might like to invite/include also.
A) ask the Smiths if they mind the Jones and others being invited to the dinner/party.
B) ask the Jones if they mind hosting the Browns and the Smiths for a dinner/party.
C) arrange a separate, external event, tell everybody where and when and let whomever show up.
D) just wait and see how things work out at the time.
The problem with option A is that it presumes the Smiths are in fact planning on putting on a dinner/party as they have indicated to the patriarch. There is a precedent set for this (they like staying home, love catering for everybody, and have entertained the Brown family all together in the past). However, it would seem presumptuous for the graduate to assume the Smiths are planning to essentially throw a small graduation party. Option B would be convenient for the graduate as it's where they are staying, so they can help with arrangements, provide all of the food etc. But that could be a slight to the Smiths if they had plans for entertaining (which is entirely possible!). Option C seems the easiest, except that many of these people are not inclined to want to go out, and would find it odd spending money externally when it's much more cost effective to entertain at home. For all 3 families it's much more normal to host at home and all are used to catering for large numbers. The bigger problem here is clearly the communication, but it's basically impossible to get the dozens of people involved together and talking.
Any thoughts? Suggestions as to how other families handle this?