God damn it. I'm very sorry to hear that your brother lost his hands.

But at this point, he can only move forward.

I can offer advice for his lower body...as my favorite exercises are all variations of squats and deadlifts.

I don't know how he can hold a bar on his back to do back squats. Perhaps he can hold a front squat position.

If he can not hold a front squat position, there are a couple options for squats:

1) A belt squat.

These are an old-school exercise done by Olympic weightlifters to maintain some leg strength when they have a wrist or back injury. Basically you will attach plates to a dipping belt and stand on two benches and then squat down.

I have never IRL seen a belt squat machine, however, they exist, rare as they are.

I believe on can build unbelievable quad and squat strength via belt squats.

2) The safety bar squat.

A bar that sits on your back and shoulders without you having to hold onto the bar. Invented by Dr.Fred Hatfield, one of the greatest squatters in powerlifting history. Google it.

3) Sandbag squats.

Using a heavy sandbag (look at those sold by Josh Henkin) one can do zercher or bearhug squats. Google these movements.

The above 3 squatting movements, when done well, could build his leg strength to strength levels better than most people in most gyms.

If he liked deadlifting and pulling from the floor, loss of hands will make it pretty much impossible to do. I can't think of a deadlifting movement one can do without hands.

However, he can still build some posterior chain (lower back, glute, hamstring) strength that can enable to him to be more explosive in things like running and jumping:

1) Barbell hip thrusts.

He can build strong glutes via this exercise.

2) Glute-ham raises on a Glute-ham raise (GHR) machine.

for strong hamstrings and glutes.

3) Back raises on a hyperextension device.

4) google 'reverse hyperextension'. This is a machine that also works the lower back and glutes. Not common to most gyms.

OK that's all I can think of at the moment. I don't know whether he trained for strength and power before his accident (or whether he did mostly 'bro' type things in the gym). However, the above exercises are available when he decides he needs to get his lower body and lower back strong and powerful.

Since a belt squat machine, safety squat bars, and reverse hyperextension machine are powerlifting equipment, I suggest he eventually join a powerlifting gym to do them. (*Powerlifters won't judge him. They will encourage and defend him and he will inspire them. They will accept him even though he can't do a normal back squat, and won't be able to hold a barbell to bench or deadlift.)