Sounds like you're in a pretty good spot. 

Find a time to sit down with the older couple for an hour. Your house or theirs, likely theirs. You and your wife with farmer and wife. 

"Hey, just want to try and figure out if there's a future with me farming here going forward. I'd love that to be the case but wanted to hear your thoughts"


Look up some options on what are possibilities ahead of time. Living trust, rent to own, LLC vs sole, and much more. Do your homework before you meet with them and let them know ahead of time what the meeting is about. Then they can talk to kids and accountant and such too so you don't have as many "i'll have to see" moments in the meeting itself