Thats right its a MIL thread! Apologies! Oh and have name changed as I'm pretty sure my mnetter friend will recognise this and I don't want her snooping through my past threads!
Will try to give as much info as needed to create a good picture of circumstances. MIL met her partner about 11 years ago on the internet shortly after suffering a nervous breakdown. Both of them are alcoholics, although claim not to be anymore as they have "cut right back" 
Their house is very dirty and smells as they do not clean up after their dogs properly.
Now to her credit, she is never drunk when she comes to visit or we visit her (in the day) and has recently started working part time again so is a lot more stable than she was. DH occasionally suggests MIL as a babysitter for our eldest DD (3 years) and was saying yesterday that we should get a travel cot so she could have youngest in the future(currently 3 months).
My main concerns about overnight babysitting are the drinking. I don't think she would be able to resist drinking for an entire evening and obviously wouldn't be in a fit state to look after the children.
My other main concern is actually her partner. He is a very strange man and none of us (or DH's family) knows much about him, even after so long. However, I do know that he has exhibited strange behaviours in the past. Once when DH brought home a girlfriend his mums partner passed her on the stairs and reached out and grabbed both her breasts. He has also been known to try and convince me to join him in the pub instead of waiting for my DH to get back from the shop whilst at their house. He also talks to young women over the internet. According to MIL he pretends to be in his 20's himself so that he can chat to young women and I don't think its innocent chat.
I do not want this man, possibly drunk, unsupervised around my young DD's. I have no idea if he would be a threat to them but quite frankly I am not willing to take the risk. DH doesn't trust or like this man either but says he wouldn't be looking after them, MIL would. But MIL trusts this man so she wouldn't think to supervise him all the time and what about when she is asleep? DH thinks I'm using this as an excuse because I haven't always got on with MIL and is also very sensitive about his mothers alcoholism and refuses to admit she is an alcoholic. In all fairness this issue crops up from time to time and yet I have avoided it successfully for the last 3 years without having to create a massive family row and could probably keep it up
I don't think I'm being unreasonable at all but DH seems to think I am. So, AIBU and if not how on earth do I get it through to DH?