Hi Manuel, You're going on holidays in July which of course is high season and high in expense. Furthermore, Barcelona is much desired city break destination as well as a beach destination. Six people though; muchos dineros tambien (big money also). It is probably a bit late, but I would advise you contact some Irish holiday home owner in the region and negotiate a price.
Barcelona is an excellent location. Like I said desired city with much to see and experience. Open top bus tours a must. Dont forget to visit Sagrada Familia basilica and of course the Gaudi locations. If you have an interest in football Camp Nou is a must see place. Enjoy La Rambla and be mindful of pickpockets.
The beach in Barcelona is a step up from anything we have here. Eating out is expensive enough but nothing like a similar location in Ireland. I think you will have the family holiday of a lifetime.