Hey i ended up in the same kinda situation i bought two females but of them ended up pregnant and she had four pups so i have ended up with six, one was a boy which we had to get neutered and I've ended up with this cage. I separated the levels with correx (plastic sheet) over the holes where the ramps use to go and have a pair of piggies in each level. They also have a playpen i set up for them in the evening...
Pets at home didn't deal with our situation very well and tried to give us a 80cm cage for the four babies to live in, however they give us a large 10kg bag of nuggets and the biggest hay bale. But my mum had to kick off to get that, we ended up phoning head office before they'd even listen to us, they wanted us to give them the babies back with the nursing sow (wasn't going to happen)!
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Anyho it's a fab cage it's really easy to clean out as it has two large doors at the front on the two lower levels which i can fit my whole body in and you can take the wire top off to clean the piggies at the top out. It's also on wheels which is handy to hover underneath it. Might not be what your looking for but it sorted my problem out.
I have bought loadsa c&c grids and might re-try another build with them but with 3 levels it's little tricky.
As you only have four piggies you could have a long single c&c or double stacked one which is a lot easier to build.
Good luck i hope you find something that works for you and the piggies!