I think your mother in law needs to get laid.. Sounds to me that she feels that she missing out ..and she not getting any so for her to peek and watch is a turn on for her.. I would Buy her a vibrator for mothers day and tell her its a practical joke... maybe she will use it and that might help ..

I would also be honest with your wife as well and tell her whats going on so there won' be any confusion and anger down the road..

DL

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when life hand you an orange make SCREW DRIVERS