Yes
You can keep multiple blennies.. but they do need good room.
I have a 50 and kept 2 lawnmowers, a mandarin goby and a watchman. (Keep in mind I didnt have all this at once, I added each over time... thats probably too much to add to a new tank and the bioload might be tilted by adding that many at a time.) But over time I amassed that and they did fine. I still have the mandarin (Yes.. thats right!! I LEARNED how to keep a mandarin alive in a reef without live sand and DAMSELS competing for food!! To those who said I couldnt do it.. BWAAAHAHAHAHAHHAA)
::Sorry.. couldnt resist::::
anyways..
Yes you can.. just make sure they have enough area to do their own things.