Kateheld,I do admire your creativity and ability to express this story idea of yours.I am going to concur that certainly with only three characters being the major players that first person would be a comfortable fit for this story .Third person would of course work better if there were more characters and more of the "..meanwhile back at the ranch" settings.

I can envision your having lots of room to develop this story with perhaps some underlying currents between the man and wife surfacing as this captivity of yours at the hands progresses.Perhaps the wife is jealous of you as presumably you are younger than she is,thus her cruelty towards you throughout your time
under the control of the couple.To add to the fires of resentment perhaps you remind the husband of either the wife in her younger years or another from his past.All motivations here for the wife's cruelty to be honed to a razor's edge.

Has this couple done this to other women in recent years.If yes then they have some experience in this area,and use this experience to leverage ever tighter control over you ,not only physically but from a psychological standpoint as well.The situation you describe here would be a prime scene for
information control as well as physical confinements.As time goes by,you find being isolated by the couple's confinement,that you become insatiably hungry
for news and information.The couple realizing that you are totally dependent on them for news and info from the outside,allow you to see,hear and perhaps read only those things that would reinforce their control of you.
Lots to work with here and I do hope you will write this story as it indeed sounds like a very enjoyable story.