You could have a talk with them and explain that what they are doing is wrong (and a mortal sin).
- if they listen, great.
- if not, at least your conscience will be clear.
If they don't listen to you then maybe tell the pastor but he may choose not to confront them.
Think of how many pro-abortion politicians receive Communion with impunity. Education is the key and then let the Lord deal with them as He chooses.