Brandi,

I'm not a fan of the "weight gainer" protein mixes that have whey in them. They tend to have a crap ton of sugar in them and that's not conducive to keeping or maintaining lean muscle mass during treatment due to the effects on blood sugar and how high your father's cortisol levels must be.

I'd recommend an organic whey protein powder as whey has the fastest uptake and highest leucine content of the other forms of protein. As far as doseage I'd be looking at 1.15-1.5grams of protein per pound of bodyweight daily as his body is in massive demand of amino acids during and recovering from treatment/surgery