If you can't get a C&C cage, the midwest habitat is also a good option. They're sold at petco, petsmart, chewy.com, amazon, etc...
It comes with a divider, which could be used to separate the two girls if they continue to misbehave, or you could keep one in the old cage and one in the midwest habitat. With the divider though, both halves are a little smaller than you'd want for just one guinea pig.
I'd say based on your pictures, it looks like there might be something going on. However, without going to a vet to get xrays, nothing can be said for certain. Since you said that a vet trip is not an option, I'd listen to bpatters who always gives very sound advice on this forum.
They're young, so you should be giving them extra calcium in the form of parsley or a little bit of alfalfa hay and that would really be the only extra thing that would be recommended for pregnant guinea pigs. Maybe give parsley a couple times a week if you can. It's usually very inexpensive at the grocery store, less than $1 for a bunch that would provide a few servings. Other than that, they're pretty self sufficient and their care doesn't change until the last couple of weeks before giving birth. If they're pregnant, then you'll definitely know by that point and probably be able to see the babies kicking. At that point, just be sure not to handle them a lot because it's potentially (but unlikely) harmful to the babies and the mamas could be mildly uncomfortable as they get close to giving birth.
All that being said, I want to reiterate that we can't say for sure without an xray, but I wouldn't worry too much about the '"what if's" and just focus on enjoying your new guineas. If they're pregnant, you'll know soon enough.