Dublin is EXPENSIVE.
It should be possible for you to support your family on 30k in Dublin, but it make take some sacrifices, depending on your lifestyle.
The area around St. Jame's Hospital -dublin 8- is arguably not the best in Dublin, but even there a two bedroom apartment/house will not come cheap, probably starting at 1,200-1,400 EUR.
In my opinion 2 bedrooms for less than that is v. hard to find, even commuting 1hr out of town. (With traffic these days 1hr commute may only get you 10 miles away from town!)
Add to that the cost of public transport, utilities, and food and you are talking a lot of money. Sorry if this all sounds very negative, but it is based on my experience of living 5 years in Dublin!
Have a look on www.daft.ie
for an idea of the cost of housing.
And here is a map of the dublin postal area codes:
http://upload.wikimedia.org/wikipedia/c ... blinPC.svg