Churches have various groups within them, and you could call each of these groups a little church. But that’s not what we’re talking about. That’s not dual church membership.
If you are part of a Growth Group, that Growth Group and especially its leaders are part of a congregation/campus, and those congregations are part of the church which the Holy Spirit makes certain men/elders responsible for. The group of 10-15 you meet with are not an independent group. The leaders have been “appointed” by the church eldership. When you submit to your group leaders, its an expression of submission to the elders who appointed them.
And refusing to submit to your group leaders is an expression of refusing to submit to your elders/pastors.
So if you’re in one churches’ small group, but you go to another church on Sunday… which elders are you submitting to? Both? or Neither?