It can work, but you need to go slow.
First, Quarantine, quarantine, quarantine! You should keep the new ones seperate from your two for a month. This is always a good idea and even more so since you don't know what happend to your 10 pullets.
Second, after quarantine is over it's usually better to introduce them slowly. If you can, rig up a run where they can see each other but not have actual contact.
Third, since the new group is going to be so much larger then the original one I'd intoduce two of the more docile or mid-ranking hens from the new group into the old one. I like to do a trial run during the day time when I can supervise, if it goes pretty well--some chasing and pecking is ok, just as long as it's not relentless, I put them in for good at night. After that add to the group keeping the number roughly equal until you have everyone in the same pen. It takes awhile to do it this way, but is safer and less stressfull then just throwing them all together and hoping for the best.
Good luck!