Family equity

I own a house (and have done so for more than seven years) with my brother who lives in London). He got married last year and would like to use part of the equity in the house to purchase another property for him and his wife. I initially agreed if we could do so without me being liable for either our current property or any future property, however it doesn't seem this is possible to do this? So I was wondering if it would be possible for him to use the equity in the property to buy me out? The house was bought for $260,000 and has been given a QV of $405,000 (Manukau) I did suggest he buy me out last year, but he doesn't think he can't afford it. I would rather sell and go our separate ways to be able to do our own thing, but again, my brother doesn't want to do that. Is there any way I can force any of the above? I.e. Use the equity to buy me out -buy me out -sell and go our separate ways?