Numbers don't tell if it's twins or not. All my numbers were "normal" for a singleton pregnancy. The only way you'll know is to get an u/s. Even listening with a doppler won't be accurate. When my mom was pregnant with me they kept hearing two heart beats. Hear...my heart was echoing off of my moms uterus.
The twin numbers I remember were from my first beta but it was at 14 DPO, and they were in the 400s. But then they tripled and tripled and tripled again, which was the only clue I had that there might be multiples until the ultrasound. The doc said the number itself was not that significant but the rate of rise was more of an indicator. However, I don't know if that was just his opinion or based on actual statistics.
I hope you get what you want!