I have 3 hairless, 2 males and a female, and none of them have health problems. My last hairless girl, Harry, lived to be over 4 years old and was VERY healthy(if you didn't count the mammary tumors and subsequent surgeries 4-5 times) until her liver just failed from old age.
Just from looking, your two girls look healthy, just a bit thin, especially the girl in the hammock. Hairless rats have very high metabolisms to be able to keep their body temp up, so they require a bit more protein and a bit more fat in their diet to keep up. What is their diet like?