Non-British citizens can come to the UK for a long-term project and make it your permanent home by joining your family in the UK
Joining the family is mainly reserved for the spouse or a durable partner of a UK citizen, a person with indefinite leave to remain or an EU national with settled or pre-settled status. In some limited circumstances, there is also an immigration option for a parent of a British child. The route for adult dependent relatives is reserved for extreme compassionate circumstances – where the person you want to bring over to the UK requires help with daily living tasks and this help is either not available or not affordable in the country of their habitual residence.
There is another option known as UK Ancestry visa which is for Commonwealth Nationals who have a British born(born on the British Isles) great parent. There is no age limit for these visa applicants but they have to demonstrate intention to work in UK and fund requirements also there to support themselves while searching for employment. Partner and children of the main Ancestry visa holder can apply for a visa at the same time or join the main visa holder later and have certain advantages in comparison to dependants in other visa categories