Would you tell them about a couple who was divorced and remarried without annulment? Cohabiting couples? Gamblers? Alcoholics? Etc.? I, personally, do not think it is my job to point out the sins of others, and i certainly don’t want them pointing out my sins. So, no. I don’t think you should say anything.
Also, since they were at mass, perhaps they have been to confession and are working out their temptation. Maybe the priest already knows their struggle.
You hypocrite, 3 remove the wooden beam from your eye first; then you will see clearly to remove the splinter from your brother’s eye. (Matthew 7:5)
But when they continued asking him, he straightened up and said to them, "Let the one among you who is without sin be the first to throw a stone at her. (John 8:7)
The only exception would be if there was blatant “flaunting” at the church that could turn others away (ex: making out in the parking lot).