Long flight overseas after several mini strokes

Hi, my dad is 80 years old with controlled diabetes, hypertension and history of bypass surgery, a small untreated tumor in the brain very close to the optic nerve, and a history of several mini strokes. He is also on Alzheimer medication for his memory . He is stable now, slight heaviness in his right leg, tends to drag it when he walks. Is it safe for him to make an trip overseas with about 12 - 16 hours of continuous flight and at least two changes of planes? What precautions can be made to ensure his safe arrival?