It is quite obvious that God the Father, Jesus the Christ and the Holy Spirit all work with Satan. Or more correctly that Satan works for God.
God (the Trinity) has a plan. That plan as described in the Bible includes Satan. For the implementation of that plan God gave Satan dominion over the Earth.
If I give someone authority over some part of my property as part of my plan it is obvious that the person is doing my bidding. That person is working for me.
But in the context of the post, one was being charged with denying the Trinity by denying the RC deuteros under the premise that it had been in the Old Testament for about 1800 years. Which was both a fallacious premise as well as a logical fallacy, as explained .