Is it smart to bring a baby (or puppy) Shitzu into a family of 2 adult boxers?

I have 2 Boxers, one female, one male. The female is five years old, the male is 3 years old, my female boxers body size is large, and my males body size is extra large-extra extra large (both purebred). And me and my dad decided to get my mom a puppy Shitzu for her birthday gift, but I personally have been having a multitude of second thoughts about this. My male dog just loves to be around people and children, he's a licker he loves to lick people, but my male dog has really never been near another dog. My female dog loves to be around children and her "owners"(me and my parents), shes over protective when it comes to children and babies, and when we take her to walk shes "afraid" of people, and would bite them if she were alone, she also have never really been near another dog. Can I get some enlightenment on this situation? Is this a Bad or a Good situation? We will be getting this baby Shitzu when it is 6 months old.