Property dispute help

I have a property dispute with my brother concerning properties in UK. Initially, the property was solely under the my name in 2018, used for a 5-bedroom HMO business. In 2023, the property was converted to joint ownership with my brother, who then used it to secure a joint mortgage for acquiring another property. All properties' mortgages are paid through rental income, but the client has not received any rental income, as the brother believes he is entitled to it for managing the properties and paying the mortgages. I want some legal advice on what is the best action to do. Thank you