I didn't visit Hotelier, we were walking on the beach and saw Las Arenas from there... it looked nice. Someone recommended it to my dad so that was why we wanted to stay there but it was full. I see on their site that they only have double rooms so I'm not sure if they're able to accomodate 3 people.
We stayed at Las Pocitas and it was nice... The food was good, the rooms were nice, clean and had a rustic-beach feel. Like most hotels, it had a pool.

It might be a good idea to check out hotel Punta Sal (http://www.puntasal.com.pe/index_en.html) as well (not in Máncora, it's a bit further north, in Tumbes). It has bungalows/suites that can accomodate 3, all rates include meals (but not drinks). We stayed there a few years ago and it was a nice vacation...