A person counts as a "family member" if he / she is:
- The EEA National's spouse or civil partner, or
- Their direct descendant (including descendants of their spouse / civil partner) - ie son / daughter / grandson / granddaughter / this includes step children/grandchildren / adopted children/grandchildren, if they are:
- under 21, or
- dependent** on the EEA National or their their spouse / civil partner
**Dependent in this context means receiving 'material support' from someone to help with the basic necessities of life - though it doesn't have to be financial and doesn't have to cover all their needs. They have to actually receive the support. CIS 2100/2007
Some 'extended family members' can be treated as a family member. But these WILL need formal documentation to exercise their rights to benefits - a registration certificate or residence card.
Who is an "extended family member"?
A person who is not a direct 'family member' (as above) can be an 'extended family member' if he / she:
- Has been issued with an EEA family permit or registration certificate or registration card as an extended family member; AND EITHER
- Is an unmarried partner in a "duly attested*** durable relationship" with the EEA National; or
- Is a relative who "strictly requires the personal care of the EEA National due to serious health grounds" is provided with personal care (eg personal hygiene or preparing meals) by that EEA national or
- Is dependent on them and certain other strict criteria are met - complex rules - seek advice.
***Duly attested means confirmed in writing, and the UK Border Agency must be satisfied that this is a durable relationship - generally the relationship must have lasted two years or this can be shortened if there are children.
What if the family member is not an EEA national?
This makes no difference to their status: they still take on the status of the EEA national as long as they are classed as a family member.
In practice, a non EEA family member will need to obtain an EEA family permit in order to enter the UK, but there is no limit on the period of his / her stay and no conditions can be placed on his / her entry. Information from the government website here. It is wise to obtain one as it acts as evidence of status - especially if they later cease to be a family member but need proof of previous relationship eg if attempting to show that they acquired permanent residence status.
Note however that extended family members MUST have a residence card - or registration certificate if they are not an EEA national themselves- to prove their rights as an extended family member, and particularly before they can apply for permanent residence status as an extended family member of an EEA national.
IMPORTANT NOTE: non EEA nationals whose right to benefits are solely through being a family members of an EEA national will need to apply for "settled status" to retain their rights to benefits after Brexit.
What if the non EEA national is the family member of a British citizen?
These rights only apply where the British citizen can be treated as an EEA national, and is 'bringing his/her EEA worker rights back to the UK with him/her': these cases are known as Surinder Singh cases after the UK case that established this ( 1 FCR 453,  Imm AR 565) .
In order to qualify under these rules, before returning to the UK:
- The British citizen must have been living and working (or self employed) in an EEA State;
- If the family member is a spouse or civil partner, they must have lived together in the EEA State;
- The British citizen's "centre of life has transferred" to the EEA State.
Factors determining whether the "centre of life has transferred" include:
- The period of residence in the EEA State;
- Whether their principal residence was in the UK or the EEA state;
- Their degree of integration in the EEA State.