We have greyhounds. We started with one, and we lasted three months before making the trek back up to the kennels. Greys in particular really thrive with another chum, since they spend so much of their time with other dogs, when they are racing. For us the biggest jump was going from two to three. Now we have four. 
I found it very easy to go from one to two - but issues you want to consider would be:- Walking - Who currently does the walking? Is your 14mth old dog currently good on the lead? How would you walk two dogs together if you are also wrangling 3 small DC?
Money - v important - be brutally honest. Can you afford the extra insurance, food, wormers, kennel costs while on holiday, etc etc Even if you have insurance, most dogs seem to have a knack for needing minor vet treatment that is just the cost of the excess in the month when the car also needs new tyres, the boiler blows up and the kids need new shoes.
Cover/help - depending on family circumstances, you might have a friend, family member or neighbour who is willing to pop in and help out when you need to be somewhere else or even for pup to have a little sleepover. Many folk who are happy to do this for one dog are understandably more reluctant to do so for two, and considerably less for multiples. Think about your support systems and how they will cope. If they can't/won't (and there is no reason why they should) then you will be back to teh money issue and thinking about kennel costs if you need a weekend away/day out etc.
Noise/mess - yes, it seems mysteriously to be a lot more. But with 3 DC as well, this may be less of an issue!
Good luck!! 