I'm dating multiple girls at one time.
Have you told them about each other?
No they don't know anything about it.
It's dishonest to date multiple women at once and not tell them. Once you start dating seriously, people are expecting you to enter a faithful relationship, and it's a violation of that trust to date lots of people.
I'm level 4, they can date me and I can date them when they take notice of me. It's not like they will know the truth anyway.
I'm not sure what you mean by Level 4, but I have to warn you that they will find out, sooner or later.  When that happens, you won't only lose the trust of the girl who found out, but also of the girl that you wanted to be with in the first place.  It's not worth the risk, so once you find someone that you connect with, you should politely end the other arrangements.