General Information:

Here "we" refers to John and those with him and does not include Gaius. (See: rc://en/ta/man/translate/figs-exclusive)

Beloved

Here this is used as a term of endearment for fellow believers. See how you translated this in 3 John 1:5.

"do not copy the evil things that people do"

There are words left out but they are understood. AT: "but imitate the good things that people do" (See: rc://en/ta/man/translate/figs-ellipsis)

"belongs to God"

"does not belong to God" or "does not believe in God"