Obviously, it is really hard to give solid advice over the screen, but a few ideas for you....
-Exercise bike sounds great, no impact, and will improve ROM and strength
- Stretches, as getting shoes and socks on sounds more like restriction.
- How are his scars? Might need some scar tissue massage
- A really good idea is hydrotherapy. Especially for his gait, and if he has pain. This basically takes away gravity, which make it a lot easier for him to concentrate on improving his gait. The longer he walks with a limp, the harder it is to get rid of it, plus all the added stress he is putting on the other side and his back. It's also a really relaxing way to do some stretches, and if you have a few floats, can do strengthening exercises as well.
Hope that helps a little!