My husband & I have an XBox One S & have a friend with an Xbox 360. We want to play Borderlands. Is that possible?
If I understand your question correctly, you wish to play Borderlands on your Xbox One, by borrowing it from a friend who only has an Xbox 360.
If that is the case - yes, you can play it. There is a set list of games that the Xbox One is compatible with from the Xbox 360, and Borderlands 1, and 2 are on that list.
However, if you are talking about the reverse, or even cross-platform play: no, that is unfortunately not possible.
XBox one games cannot be played on XBox 360. Not only would the newer games overwhelm the hardware of the older XBox 360, but the 360 cannot even read the One's game discs. The XBox One games are normally on Blu-Ray discs, and the XBox 360 cannot read blu-ray discs.