ólann na buachaillí shows a correct translation of: 'the boys drink'. What would be the difference between this and 'the boys are drinking'? In english 'the boys drink' means that that is something that they do but doesn't necessarily mean that they are right now whereas 'the boys are drinking' infers immediacy to the action.
Wiktionary says it is on the first syllable "bua": https://en.wiktionary.org/wiki/buachaill%C3%AD
Also, this beginner's guide says that words are normally accented/stressed on the first syllable (with some few exceptions) unless we are talking about Munster (Southern) Irish: http://www.standingstones.com/gaelpron.html
The boys drink would end up being a different meaning then the boys are drinking because the boys drink could be present but not now, meaning they are drinking something but they aren't putting it in their mouths, unlike the boys are drinking that could be they are drinking currently not they are having that drink. Also the words are different if the answer was the boys are drinking it would end up as a different question instead of Óllan na buachailli.