How to redirect traffic to 3proxy for different users?

Question

proxy

Hello
There is a task in 3proxy to set up "resolving" traffic by username.
Could you suggest how to organize it correctly?
That is, it is necessary that users user1, user2 and user3 are redirected to one parent proxy, and users user4, user5 and user6 are redirected to another parent proxy.
Was supposed to do it with allow and parent like this:
allow user1,user2,user3
parent 1000 http 192.168.1.10 3128
allow user4,user5,user6
parent 1000 http 192.168.1.11 3128
proxy -n -a -i192.168.1.1
However here on the toaster, people told me that this is not correct and you need to run several copies of 3proxy.
Whereas? Tell me please.