Hi Misty,
Disney's Port Orleans Resort - Riverside is a fantastic choice! I believe that your family will really enjoy your stay. In response to your question regarding a room request, I recommend that you do two things:
1) You will want to make sure that your husband's knee replacement surgery and mobility challenges have been noted in your reservation. If this hasn't been done yet, give the Walt Disney World Resort a call at (407) 939-5277 and ask to speak with a travel planner. Be sure to have your confirmation number handy when you call. Simply ask them to make a note of your situation and corresponding request in your reservation.
2) Exactly 9-days prior to your arrival, call Disney's Port Orleans Resort - Riverside at (407) 934-6000 and ask to speak with the "Room Assigner". You will want to re-iterate your request at this time. Just to be absolutely sure that they have received the request, I recommend calling again 3-days prior.
While room requests are never guaranteed, Disney does do their best to honor them based on availability at the time of your arrival.
Thanks for visiting the Disney Parks Moms Panel and please let us know if we can assist you further.
Wishing you magical memories,
Kaylene