I have spent a long time reading this thread from beginning to end. Some absolute jaw droppers on here! The Mexican house thief!! The dog towel lady!! The Alegerian holiday guest!!! 
My bil (dh's brother) has the brassiest of any neck, I have ever had the misfortune to meet! Thi is probably going to be quite long, so well done if you make it to the end.
11 years ago when he was 30, he was slung out of his flatshare situation for non payment of rent and bills. Mil covered what was owed, and to save him from getting into any more trouble, offered for him to stay with her and her dh (sfil) until such a time as he could sort himself out.
Now...it's worth mentioning that mil and her dh live in the family home that her dh grew up in. He moved in with his own (first) wife and children when his parents became infirm, to look after them, and he raised his own kids in the same house after his parents died. I think he has lived in that house for some 40 years now, not counting his childhood.
Anyway - he was agreeable to bil moving in for a bit, and for a while everything was ok - bil didn't offer anything up by way of digs (even though he had a full time job), but they overlooked it, only too happy to help out. Sfil mentioned to me on a few occasions how lazy and entitled bil was, not lifting a finger to help, and lying in his bed whining about being ill all the time (bil is a hypochondriac, and just has to have something wrong with him all the time) but because he loves his wife, he was prepared to live with it and not interfere.
"I'll just let mil deal with him - it's no skin off my nose."
After about three years of staying with them in this fashion, bil announces that in three days, he has an online friend flying in to stay for a week. An American woman that he had met on facebook and struck up a friendship with. Mil and sfil tell him he was very presumptious not to clear it with them first before she booked her flights, but nevertheless, they gut out the spare room for her (no help from bil - he is 'too tired'), and accept they are getting a houseguest.
The woman arrives as scheduled, and as soon as she is through the door, holes up in bil's room and refuses to come out while bil is at work. Mil and sfil get on with their lives, with an uninvited guest who won't speak to them, lurking upstairs. The week comes and goes, and still the American woman remains. Mil tentatively approaches her and asks how much longer she is planning on staying, only to be told that the visit is in fact, for two months, and not only that....but that she and bil got married last week, and she was now his wife!!
Of course, none of us were invited to the wedding that we knew nothing about, and there was shock all round that he could be so utterly reckless as to marry someone he had known in person for all of a week! Not only that, but he had not even extended an invitation to his own mother, from whom they were both syphoning off, eating their food, and paying nothing towards their keep.
After the two months were up, she fucked off back to America, and promptly demanded that bil send her regular money to pay for a nursing course it turned out she wasn't doing. God knows where the cash went (it was thousands) but after a year she divorced him because she met someone else anyway.
The years wore on, with him staying with mil and sfil for free, and working full time. His job changed and he was by this time, on permanent nightshift.
Bil demanded that there be no noise at all during the day, as he had to sleep...so sfil's activities were curtailed in his own house. He was no longer allowed to use power tools or listen to the radio, as it kept bil awake, and any visitors they had were made to feel unwelcome by bil glaring at them and slamming doors because he had been woken up. This included dh and myself, and our children. We live just around the corner from mil and sfil, and pop in often. After being subjected to the glaring and slamming routine once, I chased after him and told him to get his own fucking house to rule over.
After that, I was dead to him. He refused to look at me, never mind talk to me, and visitations became extremely tense, to the point where we stopped going round, and mil came to us instead.
Dh and I started to discuss the fact that over 10 years of staying with them, bil had manipulated and worn them down so much with his tales of woe, and victim complex, they had lost sight of what was normal. We gently urged them to kick him out to fend for himself (he was 40 by this time) but he had such a tight grip on them feeling sorry for him, they were unable to see the wood for the trees, and although they were miserable, they couldn't see their way to getting rid of this dreadful bully who lorded it over their house. Mil was convinced he could not cope alone, and sfil went along with it so as not to upset her. He was becoming quietly furious though, and I could tell the shit was going to hit the fan.
Eventually it did - and how! Once again bil announced that he was flying a woman over from Argentina for a two week holiday over Christmas, with only days of notice. Once again mil gutted out the spare room with no help from bil who was still 'too tired'. Once again a total stranger turned up at their house to stay.
Wise to him from before, as soon as she arrived, sfil asked her how long her visit was for, and lo and behold it was another two month guest!! Sfil challenged bil on his lies, and bil insisted that they had heard him wrong and he HAD told them it was for two months this time, and that sfil was just being vindictive by insisting that bil had clearly said two weeks, NOT two months. He accused sfil of driving a wedge between him and his mother, who didn't know WHAT to do, as she felt her loyalties were being torn.
Well that was it - sfil hit the roof and and then some!! He called the pair of them down from bils room, and told them straight that he would be taken the piss out of no longer. He laid out new house rules, whereby bil would contribute x amount to the household, cook his own meals, wash his own clothes, and that he (sfil) would listening to all the radio he fucking liked, and he would use power tools from dawn till dusk if he damn well felt like it, and that bil's reign of terror was now at an absolute end, and if he didn't like it he could fuck off and find someone else to sponge off for the next decade.
Bil was outraged!! He could not believe that sfil would dare stand up to him, and he immediately packed a case and moved himself and the Argentinian into a hotel, saying that he wouldn't stay there and put up with sfil's shit if you paid him! Of course, he could easily afford the hotel, because he had spent a decade paying for nothing himself.
Sfil told him that while he was in the hotel, he'd better start looking for alternative accomodation, as he was never setting foot inside his house...that's right laddo...HIS house, as a resident - ever again.
The Argentinian woman cut short her trip by a month after becoming unwell (she suffers from Crohns disease) and apparently that was sfil's fault too. According to bil, sfil's 'bullying' upset her so much, it exaserbated her condition and ruined their time together.
Bil did find himself a flat...and today, a year on, he still refuses to speak to sfil. If sfil is to be in attendence at a family gathering, bil won't go. He tells all and sundry that sfil threatened him, and that sfil is unstable and he is frightened of him, and that he's worried for his mum being married to such a brute.
He now attends a bi-monthly support group for the adult victims of parental abuse. 
How's THAT for a brass neck?