Directive 2004/38/EC defines a “Family member” (in point 2 of Article 2) to be one of the following:
“family member” Notes and interpretation (a) the spouse; A partner in a legal same-sex marriage should also be considered a “spouse”. See discussion on same-sex marriage. (b) the partner with whom the Union citizen has contracted a registered partnership, on the basis of the legislation of a [EU/EEA] Member State, if the legislation of the host Member State treats registered partnerships as equivalent to marriage and in accordance with the conditions laid down in the relevant legislation of the host Member State; This applies when the member state treats registered partnership “as equivalent to marriage”. Where that is not true, the partner is not considered a “family member” in this definition, but still has a right of entry as a beneficiary (see beneficiary below). This only covers registered partnerships done by an EU member state. Registered partnerships done in Canada or the US would likely be handled as a beneficiary (see beneficiary below). (c) the direct descendants who are under the age of 21 or are dependents and those of the spouse or partner as defined in point (b); Children (or grandchildren!) under 21 or those who are older than 21 but still dependent (e.g. students supported by their parents). The child can be of the EU citizen or of the non-EU citizen. This would include a child from a previous relationship or from before the EU-citizen obtained their citizenship.
(d) the dependent direct relatives in the ascending line and those of the spouse or partner as defined in point (b);
Dependent parents and dependent grandparents of either the EU citizen or of the non-EU spouse or partner. Dependent usually means financially dependent, though there may be other legally reasonable interpretations. For non-dependent parents, see beneficiary below.
These are the people who have the easy-evidence route through the Directive. They can usually prove their relationship with a simple document, like a birth certificate or a marriage certificate, that legally documents the family link. These “family members” (as the Directive states) “enjoy an automatic right of entry and residence in the host Member State” when they are with their EU citizen relative.
There are other people who are also direct beneficiaries of Directive 2004/38/EC. These are people who do not fall into this explicit definition of “family member“, but who are none the less “part of the family”. See the information about Other Beneficiaries of Directive 2004/38/EC