
I think I have probably more experience than anyone else here on this subject as this is what I have:
Arnie & Matilda, crossbreed littermates aged 10 years
Rio & Z, Malinois littermates aged 6
Roxie & Rocco, Malinois littermates aged 3
Dot, Fame & Rona, Malinois littermates aged 16 months
Molly & Harry, Papillon littermates aged 10 months
and not ONE of these cases was by choice, it was always circumstances i.e. having to keep an extra pup when no suitable home appeared.
Each case is different but in a nutshell, having two puppies take away ALL the fun. It is not enjoyable AT ALL. You have to work twice as hard, as you have to eveyrhtign twice, You CANNOT take both to training classes together, as it simply doesn't work -they need to be split up. You have to walk them separately so they don't get too dependent on each other, and you cannot lead train two at the same time. And the bond between them never, ever breaks -I am absolutely DREADING the day I first have one die as I don't know how the survivor would cope, having been so close for life.
It CAN be done, of course it can, but it's not something I'd ever choose. And my examples above show pretty well how it works, as each one is different to the other:
Arnie and Matilda even at 10 years of age are totally dependent on each other, and even now, you cannot really walk them together as they forget about everything else but each other -they turn blind and deaf to anything else. On their own, they are very obedient. I once let both off on a tarmac lane and they were so keen to race each other that when they stopped suddenly, Arnie sheared the skin off all his paws and couldn't walk properly for weeks. Siblings ALWAYS want to compete -and of course if of the same sex, this can eventually lead to fights.
Rio and Z are no problems whatsoever! Reason: I only kept Rio as a pup, Z wet to another home then came back aged 20 months. So they spent all that time apart and therefore did NOT develop the sibling bond -the time apart was enough.
Rocco and Roxie are problem dogs both of them, have had to have a lot of specialist training etc, but I have recently come to the conclusion I have to give up on them and realise they will never get better than they are now. They have fear issues, they don't come back when called, all sorts, and we did everything right with them from day one as we knew we had to. It still didn't work. So neither can be shown or worked and certainly never, ever bred from.
Dot, Fame, and Rona are the mad triplets. Spend all day playing and as soon as they see you, they launch themselves at you -three Malinois running at you and grabbing your arms (thankfully they have surprisingly soft mouths!) is quite something. Here it all HAS worked, but boy it has been hard work and still is, and because of them, I am delaying having another litter for an extra 2 years to what I normally would do, as these 3 need so much time still. I kept Fame, Dot didn't get sold, so had two. My husband helped a lot and we went to 3 different training classes, walked them separately etc etc, took them everywhere, and although they love each other and play a lot etc they are NOT as dependent on each other as the older siblings are -we learnt by our mistakes and realised we had to triple the efforts which believe me was very hard work indeed!! (And NO fun!) Then aged 14 months Rona came back to us so suddenly we had 3. Now as she had been away for a year that helped a lot, she'd had the individual attention, but as she was still so young when she came back, she also instantly reverted back to being in the litter, the dogs knew instantly who she was and the 3 of them are now inseparable and do eveyrhtign together just as if they were still 8 weeks old. And it truly is mad, and as they are still young enough to need a lot of training it's made it difficult as there are only two of us that can train but there are 3 dogs needing it!
Molly and Harry actually are no major problem being toydogs and an easier breed -but still they had to go to separate training classes (Harry to general training, Molly to ringcraft), have separate walks etc.
It's SO nice to have ONE puppy, to train it and get to know it. It's so NOT nice to have two.