In my experience my girls didn't really like the two story cage maybe it was just the one was getting older but they only used the top part (a 2x4 minus the hole for the ramp). The bottom is the only part of the cage that counts to square footage so it should be large enough for your boys to get along. I would suggest experimenting to see if your boys like the idea of a ramp etc. Good luck!
I have a two story for my boys. They are very active so they love to run around a lot. I think they really enjoy going up and down the ramp and I feel that gives them good exercise. I made sure my bottom floor is very large to make up for the fact that a top level takes away from the bottom floor a bit. I think you should try it, I bet they would enjoy having lots to do.
I always have two stories as I like to keep the kitchen seperate from everything else. However, two stories DON'T count for square footage, so you would have to make sure your bottom is the proper amount THEN add lofts.
Since you have boars, they require more space, you should probably get either a 2x4 or 2x5 cage.
I have a 3 story and my 2 girls love it. They like running up and down the ramps. It all depends on the piggie. I agree with PrincessAngel, and see what they prefer.
I have a one level right now, but I'm soon connecting my 3X5 cage by an external ramp to 3X4 "basement" which will have hay and pellets etc. I want to make the bottom level a 4X5 ( what I have under there just for a couple days to satisfy my curiosity for how the pigs would like it) but I can't because I need the storage space under my cage.
My two girls are in a single level 2x4 for now. I am thinking about adding to it and making it a 2x5 with a 1x2 kitchen but still a single level (it would look like an L). I prefer the single level because it's easier to clean. But I don't really have any experience with 2nd levels.
Mine is two levels, but it is hard to put the fleece on the second level. My daughter has trouble doing it and since they are her piggies, she tries really hard. But they love running up the ramp and I think it's good exercise and it keeps the hay in one place and then allows a full area downstairs to run. We use hanging fleece for hidies so no floor space is taking up with hidies, so they have the full 2x4 downstairs -where the ramp sits to run around.