There are a lot of guides and information on here which show why piggies need a large floor area to live in. All of those would be useful to show the other members of your household.
The Midwest for the girls is the minimum size, so while not huge, it does meet welfare standards But they would benefit from more space if possible. A 2x4 c&c is the recommended size for a sow pair.
The cage for the boys, however, is below the minimum sizes for boars. I think your piggies are only young so once they hit their teens, this is when issues can arise - while character compatibility is the most important factor, space is a huge issue for boar pairs. A Midwest cage is 120x60cm but a pair of boys should not really be in anything smaller than 150cm. A cage measuring 180cm is best. Lack of space between a boar pair can cause their relationship problems and if they fall out over lack of space and then they would need to be separated, so you’d end up needing three separate cages which would then take even more space.
A 2x6 for the girls would be a lovely size, but if taking up space is your family’s concern, then for a sow pair, the cage doesn’t need to be that big, a 2x5 even would be nice but really a 2x4 would be ideal for them.
Two Midwest’s together for the boys would give them more than ample room but again, if taking up space is the concern, then they would be absolutely fine in a 2x5 c&c.
As a result and as c&c cages can be stacked, if you get two 2x5 c&c cages (180x77cm) and then stack them, both pairs of piggies will have the ideal cage space but will only take up the floor space of one cage.
Its also best for boars to be kept well out of sight and smell of sows. Stacking cages makes this easier as you must keep the girls at the bottom and the boys on the top cage. That way, the risk of sow pheromones drifting to the boys is much reduced.
Cage Size Guide
A Comprehensive Guide to Guinea Pig Boars
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
