Not necessarily. Obviously without knowing the cost to settle the remaining finance, it is difficult to work it out, but loans are cheap just now. 3.6% on compare the market. A £10k loan comes in at £182 per month over 5 years, so may or may not be more expensive really. I often find it isn't really worth PCP-ing a 9 month old car because you don't get the better "new car" interest rate, or the new car discounts from the dealer. So he may well be cheaper with an actual loan.
That being said, I'm kinda with you here. I would personally put the car back, and take whatever financial hit you have to take. I certainly wouldn't trust MY brother to make payments in full and on time. I could see a situation like this causing more problems than it's worth. I would suggest he either takes a loan to cover the outstanding finance, or goes looking for his own deal.