Well I think we have a general idea of what everyone has and what we could do with organizing a game for everyone.So first of all we need to try and figure out what game we should all try and play together, and from there we can work on further requirements such as mods that enhance the flavor of the game or extend playtime.
I have a couple of ideas that can be considered while deciding to pick games, or use a combination of them.
We can do a single game, playing until we finish up or get bored.
We can do an extended world timeline, (e.g. trying to go from CK2 to EU4 for plenty of years of gameplay), but also can result in issues for players who cannot continue.
Of course we will also have to agree on some basic rules based on the game we collectively choose to play for mechanics that we can use (e.g. political influence and coups in HOI 4 being restricted to a degree) and the procedure for when a particular player does not arrive. For now (this can be of course adjusted later) we can organize a general time on a particular day like for example a Saturday night or when all players are present and willing to play, and also specify how to proceed when players are absent, such as if there are 6 players total and 2 are missing, the game can continue leaving the countries in control of the AI.
And of course finally not everyone will have good run, so with agreement from the majority of players, if someone is really frustrated and wants to switch countries (of course this shouldn't be on a whim) we can approve allowing the player to choose who to continue playing as, but it should also find a balance between respecting other players ambitions (don't be a douche and take a country a player is ready to go to war on attempting to ruin their experience) while picking a nation that as long as everyone approves or a sufficient explanation is given, can be chosen and played. (we should appeal to have fun and have somewhat balanced gameplay, but I don't want to see a game grind to a halt because one player wants to seize an entire area as a future game plan without any immediate means to do so, like if someone was whining at a player because they wanted to colonize all of North America and they chose a Native American tribe).
And finally the last thing I want to address and eventually come down on for rules is we should be comfortable going to war with each other. Of course it can lead to frustration and temporary setbacks, but it is actually a critical element that can lead to a game being fun, I believe a game would be very hard to enjoy if Germany and France always yelled (drowning out other players wanting to possibly speak) because of war declared or specific areas seized that the other wanted control of. Of course regulation is needed (games shouldn't devolve to conspiring with other players to eliminate someone out of the game by ganging up on him) but we need to be willing to go to war with each other, or at least undergo strategic maneuvers (e.g. proxy wars) to enhance everyone's experience further and form a timeline that is interesting for not only us to remember but others who did not participate watch history unfold.
In summary, don't be one of these people:

Do this:

Actually don't do that specifically, but YOU GET THE POINT FFS!