
I have a senior male and a junior female and then introduced a further male pup and everything was fine.
My junior female (who was then 14 months old) took to the pup straight away, however my senior male (10yrs old) ignored the pup for the first few days, however now has also formed a good bond with him. All three get on really well and will all play together quite happily.
What I did was to give my pup some time out after he had been fed by putting him in his crate with his toys and a treat. This gave the other two some time to relax away from the pup. Also if we had to pop out, he would go in his crate with nylabones to keep him occupied and a kong filled with goodies. This was because I felt he was too young to be left with free access to the house like the other two.
1) Because of the chewing factor and ingesting something that could cause problems to him
2)Because of the safety aspect in case he hurt himself playing with the other dogs or running around etc
3) To give my other 2 some time out
He sees his crate as a positive as he always gets goodies every time he goes in there and will go in there on his own accord from time to time to play with his toys or even have a sleep. When he goes on his walks the vast majority of the time I will take him out separately to my other two in order to lead train him and practice his recall and to further our bond together. Now and again I will take him with my male or female so he learns how to walk alongside them without trying to be competitive.
I have always had at least two dogs at any given time and have never found them to become too "doggy" and have always had a very good bond with them by giving them one to one sessions and making our time together lots of fun.
What I would recommend is that you give your current dogs lots of attention and fuss when the pup arrives so they don't feel left out and the pup is not elevated too high above his station as this is when jealousy could arise and make sure there is lots of one to one time with them as well. Also if you have visitors, its so easy for them to go straight to the pup forgetting about the other two dogs, I always made sure that the older dogs had fusses first before the pup from the people visiting.
I have always fed my dogs together in the kitchen without any problems. Again what I did was to ensure when putting the bowls down that they all sat and waited and the pups bowl was placed down last. If pup finished before the other dogs, I would stop him from going to the other dogs food by telling him "no" and asking him to sit. All 3 respect one another when eating and will not steal food from each other if one has finished before the other, although they will sit watching. lol This way there has never been any problems with aggression around food.
I hope you have loads of fun with your pup. It's a really exciting time. Let us know how you get on.