Mr. lybrate-user, Thanks for the query.
There can be many causes for the swelling of both the legs, like uncontrolled BP, heart related problem, kidney disease
, problem with the liver and thyroid condition particularly hypothyroidism. So it is difficult to say what may be the reason. A lot of investigations are needed to identify. Since you have not mentioned any details regarding his present complaints, symptoms and condition he is having as well as treatment being taken. Please give some relevant info, then only I can comment or advise. Thanks.