I have a male Maltese who will be 3 in May.  He is 9 1/2 pounds  

 and my little girl Yorkie is 7 1/2 months old and just under 4 pounds.  They are great buddies!  The maltese took to the Yorkie pretty quickly.  Every once in a while they fight (usually over a bully stick or some other treat) but otherwise they are wonderful together.  Their sizes really compliment each other.  The maltese is bigger but not too big to hurt my yorkie baby. 
Enjoy your two 'kids'.  You're going to love having two dogs!! 
