Ratties Ferret Kingdom, Good or Bad?

It's definitely plenty of room for your girls. Lots of ramps and such for climbing.

I would be concerned about spacing. Depending on their size, they can either squeeze out, or possibly get their heads caught. I have 1/2 x 1/2 inch spacing on my big cage, and can't put females under 6 months old in it. I had a 4 mouth old girl get her head caught! Thankfully, I was right there when she did it and was able to calm her down and get her out. But talk about heart attack. hmy:

Something else you might consider with this cage, but can be easily solved, are the "drop offs" from the upper levels. Look at it and ask yourself how far a rattie could fall, if they slipped or fell asleep on one of the upper levels.
I have a Martin's cage with similar "half" levels. I hang hammocks off the sides so if anyone slipped, they'd just fall into the hammock.

I wouldn't say the cage is not doable...but you might consider the spacing issue. If your girls are full grown and not small...you might be ok.

For two females, you might try looking at the Martin's cages. An r695 is a perfect cage (for up to 4-5 rats), durable and maybe cheaper (be sure to go with the powder coating) than the Ferret one.