
Hi Sarah,
I know it's probably disappointing to hear people advising against this but it isn't a good idea - for the puppies, your older dog or you and your mum. :-(
There will be some people who have found it manageable - possibly more so if not siblings or exactly the same age - but even many very experienced people with every training skill honed to perfection and totally dedicated 24/7 to giving separate training, socialisation etc to the pups have found it extremely difficult.
It's not just over coming their natural bond with one another - which, with the best skill and will in the world IS hard to overcome. You've probably read several threads recently from different owners concerned about the behaviour of a single 8-12 week pup being too boysterous and potentially *aggressive* with the resident adult and worrying how this may affect their puppies behaviour towards strange dogs in future. Young puppies even when carefully supervised can be very wild when playing with one another and they are potentially learning fighting skills with their naturally rough games :-(
Another depressing point about getting two puppies (same breed therefore same life expectancy) together is that a few years down the line you have two elderly dogs at the same time too with all the worry and heartache which that can bring.
Why not let your head rule your heart on this one ;-) you seem to be leaning that way anyway by the sound of your post. Get your preferred single puppy, enjoy (and control LOL) it's mad cap antics. Importantly too, allow your existing dog lots of time to get used to having a youngster around (as well as lots of time out and extra cuddles, walks etc from you) and they will hopefully be great friends. Then if you want to add to your fur family number a couple of years down the road you should have two happy, well adjusted and well trained adults to which your next hopeful can aspire :-)
I don't know how long it is since you last had a puppy but if you're anything like me you've probably forgotten just how much work they are - I usually have mine at around 5 year intervals and I'm darned if it doesn't still shock our household to the core when it comes flooding back how much havoc even the sweetest puppy causes!
Whatever route you decide - good luck and enjoy (plus grab as much shut eye as possible over the next 3 weeks) :D :D :D
Best wishes, you've chosen a favourite breed of mine too!
Teri