My son just spent four nights at the Fleet Street Hotel Temple Bar. It is in a convenient location and everything is a walk away. My son is 23 and went on his own, but he did say that there were many couples there. The area is very lively at night but according to my son, not very noisy. That may influence your brother's decision. Tripadvisor.com has much feedback on this hotel, most of it extremely positive but some saying it was dirty. My son thought it was fine. Bu then again, that's from a 23 year old, single guy's perspective, who probably thought every dorm room he lived in was clean!

Here are some links for you:

http://www.fleethoteltemplebar.com/

http://www.tripadvisor.com/Hotel_Rev...ty_Dublin.html