lupus does effect your memory and consentration. I have had symptoms of lupus since 2001 but was not diagnosis until 2006. I must tell you that since I have been on lupus drugs, my quality of life has gone from good to very poor. They may help your father's inflammation, but they do not come without side effects and some are the same as lupus side effect. My nerves in my bladder, hands, and feet have been damaged, all connected with my lupus. Although I am on several drugs I am still in pain everyday, somedays worst than other. I have taken Predisone, Methoprenisolone, Methotexate, Imuran, and Plaquniel. I forget simple things. Words that I know how to spell.
I will keep your father in my prayer. If you can afford organic food and vitamins, please try them. I have had to stop mine because I am not working due to my health, but I miss them and they really made a difference in my life. 
All I can tell you is educate yourself about lupus and this website is wonderful because no one can understand your dads problems like people who have gone through or are going through what he is/will go through. You understanding will help him so much with dealing the changes that lupus will do in his life. 