Swollen feet on the elderley?

inactivity can cause swollen feet, when people get to this age, because they are a bit achey they tend not to move as much, where it would be better for them to move more, my mother in law is the same, we live about 50 yards from the promenade, there is a bench every 50yds, yet will she go for a walk, we have said you can have a sit down every 50 yards, but unless she has to go out for a reason, she wont go, she even said what do you want me to do, walk the streets, we said yes, everyone else does, then she complains that her ankles are swollen at night because all she has done is sit on her bum all day, heat and high blood pressure can also cause swollen ankles, so he does need to go to the docs really, good luck