What Causes Weakness In Legs And Shortness Of Breath When On Blood Thinners?

my father in law is on blood thinning meds. He is 79 and can barely stand. He has always had weak legs and used a walking stick, but he has shortness of breath and he also has asbestosis of the lungs. Can you make any suggestions of how to help him? My husband an I are both sick with head colds, I am not sure if he has this, or something worse.