How to evict a family member in Scotland?

Hi, I need advice regarding eviction of a family member in Scotland.

My partner owns a house in Scotland that has been in his family for generations. He used to be in the army for about 9 years and was away for months. He let his sister live in the house but she never paid any rent. She would only top up the gas and electric meter. In the past he had problems with her and had her sign a letter from his lawyer regarding her antisocial behaviour — was messing with his post (opening letters and hiding them, he also mentioned she tried to forge his signature so he couldn’t kick her out). She is lazy, no job, sleeps till afternoon and just sits around the house doing nothing. My partner said she is a compulsive liar and has been called out on those lies countless times. He is now out of the army and is living in the house full time. I moved in last year. We are trying for a family and don’t want her to live with us anymore. I don’t want our future children to live with and be raised around bad influences. How can we get her evicted?

She told us 2 months ago she is moving out but every single time she is supposed to go, the day before or on the day, “something comes up" and she stays. She is messing with us and we can’t stand it anymore. She was supposed to definitely move out today but that never happened. My partner took time off work to help her and she just came up with excuses again. I don’t understand what she is trying to accomplish here.

Does she even classify as a tenant, lodger, etc? We don’t want to go through courts as it is such a long process.There is no tenancy agreement and she never paid any rent.

Please someone help with some advice :pray: .