I have 5 but I'm a stay at home mom. I got my first a little over a year ago and he was 8 weeks old. I got a girl(Lady) the next month, she was 5 1/2 months old. Your pup is older than my Pirogue but let me tell you what happened. He thought I brought him a real live pet. He hardly paid me any attention after that. He was happy and she was happy but I was left out. Lady is still his favorite toy.
Lady decided she belonged to daddy. I waited as long as I could and got another puppy(Autumn). I actually bought her for my husband but she chose me. I have since bought a little boy(Mr. Big) and a little girl(Lacijo, his half sister). Mr. Big chose my husband when we picked him up but he has since decided he's a mamas boy, and his sister has decided she's a daddys girl. So now I have a little girl and a little boy for me and daddy has 2 little girls. Pirogue is his own man. Well, SOMETIMES he allows me to hold and kiss him, sometimes.
LOL did I get carried away? I forgot what I was going to say. Your pup is older than Pirogue when I bought Lady, ok. He is very well settled into your family and I think if you brought in a young female and kept a close eye on the situation for a while that things would work out very well.