Further update: it was clearly stated at the time that the other dog was fine with no apparent injuries. Understandably, it may have anxiety issues after this of course.
Apparently, they kept going back/forth along my friends fence line knowing full well it was upsetting my friends dogs. It was then that my friends dog scaled their fence to get over to the other dog in question.
Please continue to offer any advice as they only have till the morning before ranger is coming.
Thank you Haredown Whippets for your reply :)