Aw, they're so adorable! I'm glad to see they all look healthy so far. Is the white pup completely white? I'm even more excited to hear that you're already planning a new cage for them.
Timothy hay is fine if that's all you have for now. It won't hurt them or anything. Alfalfa is just recommended since its higher in protein, carbohydrates, and calcium.
[*=left]"Growing guinea pigs. For the first few months of a guinea pig’s life he requires a huge amount of energy to grow. Alfalfa hay (and pellets) provide him with this extra protein and calorie source.
[*=left]Pregnant and nursing mothers. Not only when pregnant and her young are forming internally, but also for the guinea pig to provide the essential milk to feed her babies."
I've never been in your situation before so I just did a little research to try and help out. Best of luck!