# But one brother brings a lawsuit against another brother—and this before unbelievers

"But brothers who have disputes with each other ask judges who do not believe in Christ to make decisions for them" or "It is bad that brothers have such bad disputes with each other that they go to court; it is even worse that those courts are run by unbelievers"

# brother brings a lawsuit against another brother

Here "brother" means fellow Christian, including both men and women.

# brings a lawsuit

asks the civil court to judge the matter

# and this before unbelievers

Possible meanings are 1) "and the brothers have unbelieving judges make decisions for them" or 2) "and unbelievers in the community see brothers disputing with one another"