A non-EEA family member of an EEA national may be able to apply outside the UK for an EEA Family Permit to join their EEA family member in the UK if their EEA family member is exercising Treaty rights.
Or they may be able to apply to come to the UK with their EEA family member if their EEA family member is coming to the UK for the purpose of exercising Treaty rights.
There is no requirement to apply for an EEA Family Permit to enter the UK, it can, for example, be issued at the UK border.
However, applying for Family Permit in advance will simplify entry and avoid the conflict with the airline, where they may not allow a passenger to board the plane in the absence of a valid visa.
An EEA Family Permit is granted for a period of six months and the visa holder is entitled to work in the UK.
After arriving in the UK, a non-EEA national family member will have to prepare and submit the application for an EEA Residence Card, which will be issued for a period of 5 years.
After 5 years the person may be eligible to apply for Permanent Residence in the UK.