4 members which can be 4 characters from the same account and not 4 distinct accounts. All that is needed is a friend or a temporary 2nd account to invite alts.
SE would avoid a lot of that BS and ease the demand if they allowed the sharing of private houses with alts and added a chest to share things. It's possible to have complete strangers as tenants but not alts which is stupid.
The only way to share between alts is by making an fc which also comes with additional perks, especially if you get a house (fc chest which is in itself a desirable feature even without a house; workshops if people care about that; GC bonuses; quick, direct and cheap travel to access to vendors, retainers, armoire, aesthetician, menders, gardening for all, lutilities with bonuses for leveling DoH; market board without crowd noise as well as - for fans of decorating - fc rooms without the risk of someone kicking people out, etc. )