Hi Agnes -
Sorry I didn't get to finish my post..........
Remember that they are GUESTS in YOUR home. When they first bring it up, you must shut them down immediately; if you give them an inch they will take 784 miles. Just tell them you respect their beliefs, but while they are in your home, they must respect yours!
And have the phone number for the nearest hotel in your hands at all times.
Sincerely,
Maya