I'd go with your gut and go the KI couple as well.. The agent seems a bit too keen to help out the other tenant and that could be genuine or it also could be that the house they're selling has had alot of comments about prospective buyers preferring vacant possession which would most definitely prompt the agency to be much more proactive about finding them another rental asap, not that this means they're bad tenants, I'm sure they're not if the agency is willing to give them another property, just saying it could be a genuine reason for what's behind the 'good word' and urgency as the PM's could be under a bit of pressure from the Sales Team to get that property vacant so they can sell asap..

Anywhoo, regardless of all that, I'd go for the KI couple just because they were there first and sound like they deserve a fair go too