Try www.rollercoaster.ie or www.eumom.com for lots of advice from parents who might have experience of what worked for them. Think their is a twins thread on rollercoaster which might give you some useful information.
Get the narrowest side-by-side buggy you can find. It is amazing how many doors in shops and other public places can't accommodate wider twin buggies. An inch or two can make a tremendous difference.
maclaren have 2 excellent side by side models. the lighter one is better as its easier to fold. put into the car etc. the heavier one has muffs etc and some other stuff included and by the time youve bought them the prices are the same. we got a present of a 3 month old cosatto twin from someone who said they didnt need it any more (3 months? - alarm bells) it was lovely except that all 12 wheels wanted to go in different directions which meant you just couldnt push it regardless of the surface. the maclaren ones have great wheels that would turn on a sixpence and i would highly recommend them.
I have a new born and a 2 year old also and opted for Phil and Teds E3 double , which is an alternative to the side by side and tandem. I priced the double model, which you would require, at about €600 but wound up ordering in from the UK and saved €100.
Its about three years since our twins were in a buggy but we found the tandem version much easier to manoeuvre around shops etc. We had originally bought a side by side but it nearly drove the wife cracked so rather than listen to a screaming wife and two screaming kids I reckoned it was better to cough up again for a tandem buggy and let them listen to me giving out about the expense
We have a tandem and a side-by-side. The tandem (Graco) is quite heavy and robust but eats up boot space, it's good for long walks and we've had 3 in it with the biggest lad standing on the middle step. The side-by-side is a Maclaren 29" model so it fits through nearly all doors which is important and it folds to a very tidy size so is handy for the car. All things considered I like the Maclaren.