Two FOREIGN KEY constraints with SET NULL targeting the same PRIMARY table
It would seem you have cascading deletes on and you'll end up deleting someone who could theoretically be referenced in another group as a treasurer or secretary.

The group table is violating the 1st normal form. This is akin to having address1, address2 in a table.  

You need a third table GroupPersonRole that holds groupid, the person id and the roleid.

Define your person in one table. Define your group in another table. And define your role in another table. Then in a fourth, say GroupPersonRole, you can combine them and draw your FKs as needed.

What if someone wants to add more group roles? You don't want to be modifying schema every time someone gets a new idea.