Will my kitty recognize his sister (and vice versa)?

I left my 2 cats with my mom years ago. They're 16 now, Rudy came to live with us when he became sick and needed to be nursed back to health. Jasmine remains with Mom, but I'd like to bring her back for Rudy - he has fiber sarcoma and doesn't have more than a year. I have 2 other cats, who are litter mates themselves and are very close. I want to give Rudy his mate back (and will need to convince my husband) but I won't do it if they won't eventually remember each other. They were together for 13 years previously (if this helps).