You can purchase asics trail running shoes at most sports retail stores! I would suggest runners roast in Fort Collins as the people there are very smart and would be able to answer any questions about your brothers request for those shoes.
If you a running on a trail or trail-type surface, than yes, the asics trail running shoe would be ideal for a marathon. If the marathon is on a hard street surface, then I would research other shoes.
There are a number of different trail running shoes available for purchase in the market. I would recommend purchasing the Asics Mens Gel Kahana 5 running shoe as it appears to have received the best reviews.
You can purchase trail running shoes with many online and in store retailers. It is best to buy in stores, especially for a first pair, so you can try the shoes on.
You can visit the asics website direct (http://www.asicsamerica.com/Footwear/Running-Shoes/). Alternatively to get an overall view of the shoe and learn what other people have said about the shoe, you can use online review sites. A useful one for you may be runnersworld.com as it focuses specifically on running.
The ASICS Gel-Trail Lahar 3 G-TX is what you need. It is a waterproof shoe that lasts through mud and creeks on uneven terrain in all types of weather.
There is a site called Shoe Buy (http://www.shoebuy.com/narrow-trail-running-shoes.htm), which prides itself on selling many varieties of shoes. Their site allows you to search based on various criteria, making it possible to find narrow trail running shoes.
Trail shoes are shoes for running in rough terrain. They are bulky and heavy I do not recommend running with them in places were there is not rough terrain.
According to ConsumerSearch, the best reviewed trail running shoes are the Saucony ProGrid Peregrine at $90, the Merrell Trail Glove and women's Merrell Pace Glove at $110, and the New Balance Minimus Trail at $110. Note that each of these is for a different type of terrain.
The best trail running shoes have nylon puncture protection in the sole. Depending on where you are doing your trail running, better shoes will either have crampons or the ability to install them.
A regular pair of running shoes should be sufficient for trail running. But, if you are an avid trail runner, then you can find a pair of specific shoes called the Brooks Adrenaline ASR5.
This website, the 'Running shoe guru' will show you what kind of shoes are best for trail running and have reviews for you. http://www.runningshoesguru.com/best-trail-running-shoes/
Yes there are specific running shoes designed to run on trails. They are called Trail Running Shoes. They are made specifically for trail running just like street running shoes are specifically made for the street.