How to approach my aged neighbor about possibly selling to me

[David Schoolcraft]

Neighbors are in their late 80s and live directly across the street from my wife & I would love to buy them out when they're ready to sell. Wondering about how best to approach. They have been in the house for nearly 60 years and, when I've brought up that we would like to be them out when they're ready to sell, they've told me that just makes them sad to think about it. I'm on good terms with them and would like to remain that way as they know EVERYBODY. I don't know what (if any) plans they have for their property when it's time to move out. It's a quiet residential area with some town and no-wake lake, we'd like to perhaps rent out their existing small house and build a large pole barn on an adjacent lot for storing some of our stuff.

Should I approach the grown children, one of whom lives in the area but we've never had any contact? Would you suggest an approach to the neighbors? What would be best mode of approach;  offer right of first refusal, make a purchase offer right now with life estate to them, something else? Thank you.