Kentish Lass

I believe that after having P.R. for 3yrs, you can sponser UK relations to come over.....?? My query though is that my Dad is in his eighties and has had Parkinsons for many years. It broke my heart to leave him and my Mum last year when I went back for a visit.My sister lives near them and helps out a lot but is very busy with her own life. I would love to get them over here but it would have to be a one way trip. My old Dad would never be able to attempt the journey twice.