I'm not an expert, but my guess would be "separate them"

I found quite a few articles...one is attached.

http://www.growinglifestyle.com/article/s0/a2534.html

"Bernie" wrote in message
news
I just purchased two 6 packs of celosia, and noticed that in some
of the containers there were 2 plants. Should I plant more than
one of these in the same hole?

-Thanks