Start from how mice actually live together
The housing plan for pet mice is really two plans running side by side, because the sexes want opposite things. Female mice are social to their core: sisters and unrelated females usually settle into a group, groom each other, pile up together to sleep and clearly do better with company. Adult males are the reverse. Once they mature, most males will fight a cage-mate seriously enough to injure him, so the working rule is one male per enclosure. Planning housing means accepting that split up front and designing floor space, equipment and cleaning time around the number of enclosures, not the number of mice.
The females' group home
Give the girls the biggest footprint you can manage, because a group needs room to spread out, claim corners and get away from each other after a squabble. A wide, low enclosure with solid flooring suits mice better than a tall one with bare wire levels they can fall from. Fill it with more hides than you have mice, at least two water points and two food stations, so no single mouse can guard everything at once. Deep bedding matters as well: mice dig, tunnel and build nests, and a generous layer lets the group shape the space themselves. When you add a new female, rearrange the furnishings first so the home smells neutral and nobody is defending an established territory.
A solo setup for every male
Each male needs a complete home of his own: an enclosure with a solid floor, a wheel sized for a mouse, a hide he can retreat into, chewable material to keep his teeth busy and enough bedding to burrow in. Solo does not have to mean stark. Rotate safe toys and cardboard in and out so his world changes, and handle him regularly, because a lone male leans on you for the social contact a group would have given him. Keep his enclosure in the same room as the females so he gets their scent and chatter as background company. What he must never get is shared floor time with another male, even briefly and even supervised, because fights start faster than you can step in.
Siting, cleaning and the daily round
Put every enclosure in one quiet room away from direct sun, radiators and the thump of household traffic, and your daily round becomes a single circuit: top up food and water, spot-clean the wet corners, check wheels are spinning freely and look each mouse over. Males mark territory with scent, so a solo male's home usually needs its bedding changes on a tighter rhythm than the group enclosure, and leaving a small handful of the old nesting material behind at each change keeps the place smelling like his. Bar spacing is a planning detail people miss: mice squeeze through gaps that look impossibly small, so check that every door, lid and vent on both setups is genuinely mouse-proof before anyone moves in.
When the group changes
Mouse groups are not static. A female who bullies the others relentlessly, an elderly mouse who needs softer food and a lower water bottle, or a young male reaching the age where he starts squaring up to his brothers all change the arithmetic, and it pays to keep one spare enclosure on hand so a separation is a calm move rather than an emergency purchase. If you ever decide a mouse needs a new home instead, his quirks, diet and daily rhythm are worth passing on rather than leaving the next keeper to guess. A mouse's world may be small, but it runs on routine, and KinsLe's Care Teams keeps the feeding, cleaning and health-check duties for every enclosure assigned and timestamped, so each of your mice gets the same reliable care whether they live in a crowd or on their own.