I think the OP needs to clarify, as several things make no sense as written!
"my MIL has mental problems, she gets very stressed and even banned the kids from going in their house. the last time we went over our 5 year old ended up locked in their bathroom "
If the kids are banned from the house, how is one locked in the bathroom?
And if you are leery of the MIL, why was the 5 year old unsupervised?
"our beautiful lil girl ended up messing herself coz she was too scared to go to the toilet, even at home. it took months to get her clean again."
What? Months to clean her up after a mess?
Things don't add up...
“We cannot change the cards we are dealt, just how we play the hand.”
~ Randy Pausch
"There's a difference between interest and commitment. When you're interested in doing something, you do it only when circumstance permit. When you're committed to something, you accept no excuses, only results."
~ Art Turock
"We have a saying in Tibet: If a problem can be solved, there is no use worrying about it. If it can't be solved, worrying will do no good."
~ 7 Years in Tibet