A few things to consider:
1) Rents are generally higher in Fort Collins for the same house.
2) Your brother already has a loan on the Fort Collins house at owner rates. Not sure what rate he got 5 years ago, but my guess is it is probably lower than what he can get now as an investor.
3) If he sells his Fort Collins house, he will need to pay realtor fees, perhaps as much as 6%, which can significantly impact his purchasing and leveraging power going forward.
4) He might try renting out his Fort Collins home first and see what he can reliably get for it. He could rent for a while in Loveland before he makes a final decision on whether to sell in Fort Collins, and what to buy in Loveland.
Personally, I would go the route others suggested and keep the Fort Collins house as the rental, and use a HELOC or other assets to buy his new home in Loveland. One thing to be aware of though is that rental income from the Fort Collins house will not show up until the following year's tax return, so that may cause issues in qualifying, depending on the lender. The advice to start with a lender and determine the possibilities first is good.
Good Luck!