Can a pastor remarry? Yes, if his wife has died.

Can a sister remarry? Yes, if her husband commit adultery.

Can a pastor whose wife has died marries a sister whose husband commits adultery? Yes!

The matter is simple. The other preaching coworker makes it complex.

He may be thinking about 1Timothy 3:2 (Now the overseer must be above reproach, the husband of but one wife, temperate, self-controlled, respectable, hospitable, able to teach ...). But he may have exegete the requirement of "but one wife" wrong.

One wife as long as his wife is neither dead, nor adulterous, and legal married to him.

Do not put on unwarranted burden to people's shoulders.