Dog behaviours

Question
18 months ago I purchased a male and female from the same litter, we had 18 wonderful months together before our little girl died when she was hit by a car.  Last week we welcomed a 9 week old female pup into the family and apart from the first afternoon when we brought her home, our little boy has taken to her and they are fast becoming great friends.  There is a male pup from our girls litter that the owners have been unable to sell and I am considering purchasing him also.  I do not want to upset my boy though. How will a new male dog be perceived by him. How would it change the dynamics.  They are all chihuahua x dogs.

Answer
I'd be quite cautious about adding this male puppy.  Your present dog is adjusting well to the new addition and they are forming a bond; the bond between the puppies is already established and may interfere.  It is never a great idea to obtain two puppies from the same litter because of the possibility of close temperament.