Hi Gman23
5 inches in two segments are in theory possible. Perhaps you need to do it one by one to maximize the lengthening after at least more than 1 year of recovery from the first surgery.
You probably can do it sort of at the same time in Paley institute in US with 3-4 weeks gap between the two surgeries. However, in this case you need to have Stryde nails for both surgeries which will cost over $200k. If you choose Stryde nail, which I think is the best choice, you will need to think about much more budget. Most of doctors will ask you about $100-80k for one segment. Dr. Giotikas offers Stryde at lower price but he is less experienced than other top doctors.
The maximum lengthening is 8 cm with Stryde for both femurs and tibias. 8cm of femur lengthening is relatively more achievable than 8cm of tibia lengthening. For tibia, 5-7cm is a general range of gaining with Stryde, which most of femur patients can achieve 7-8 cm. If your budget is tight, you can consider LON for tibias, which costs much less than Stryde but as effective at lengthening as Stryde. However, any external device is quite painful and leaves much more scars than internal nails. I don't recommend the external method for femurs. If you want to lengthen femurs, just do Stryde and choose a good doctor for you.
Good luck!!