Warning: long and possibly boring to you.
Suzy, the relationship between your sister and you sound similar to that between me and my older sis. In addition, she always had a sibling rivalry thing going that I never cared to take part in though I'd always end up hurt or angry. I have over time just accepted that that was who she was and made allowances for it. Later, I started to just stand my ground and not give her opportunities to manipulate my feelings around the rivalry and did that mostly by keeping my distance.
My nephew (from a different sister) came to live with us as a 14 yr old with the view to staying till at least 16 and hopefully 18 yr old. Within a week of being with us he was stealing money out of our bedroom and purse and appropriating any gadget etc that he fancied that looked like they were just 'lying around' the house. He also spent a lot of energy avoiding all forms of work (schoolwork, homework, household chores, even chores we agreed to pay him for) or doing such a piss poor job when cornered into doing any of it. He then took his lying and stealing ways outside the home to his 'mates', stealing over £200 worth of gameboy stuff then lying to me about selling it on only to catch him playing the damn thing in his room a week later. The 'mate' involved the police even after I attempted to make amends. My family though blames me for his stealing and subsequent police record - because I limited his own playing with his gameboy.
I finally decided enough was enough when he went to school - the same place as my workplace - saying that my husband bullied him and he wanted to 'kill himself' which became a child protection issue and social services was involved. Being 7 mos pg at the time, like hell was I going to have my child born on the social services register or end up on list99 myself because of his behaviour.
I was thinking today that considering that they believed I was doing such a 'bad job' 9 months before he left my house - that is, when the stealing occurred. They still let him live with me until I decided to send him back and paid for his airline ticket to do so.
Since being back home, his lies have grown. My mum called my dh a 'paedophile' to me so I can only imagine what his stories have insinuated.
There were times when my dh and I felt so stressed at dealing with him, I have said some harsh truths about his background in unfortunately less than tactful ways that every one else had lied to him before . The truth but in the cold hard light like he had never seen before. my dh had also had to fight his instinct to fill him in at times. But no matter how much he was 'afraid' of my dh. Right to the bitter end he was stealing out of both our wallets. Not fearful enough in my eyes.