Hi and welcome to Healthcaremagic. I understand your concerns and I will try to help you as much as I can. His symptoms such as shortness of breath and leg swelling indicates heart decompensation which means that blood is accumulated in venous system of legs due to bad heart function. This is serious issue and you need to get him to doctor to have diuretics and medications for heart muscle. Less common this may be sign of bilateral oedema due lymph edema or kidney disorder. In this case he would have reduced urination. It is important to keep legs elevated and apply eastic compresses. ALso, measure his blood pressure frequently. His weight gain is probbaly due to fluids accumulation in body which is typical for conditions that I have mentioned so these should be ruled out. I hope I have answered you query. If you have any further questions you can contact us in every time.