Possessiva im Dativ

After the dative prepositions mit, bei, von, zu, aus, nach, seit and after verbs such as helfen, gehören, gefallen, danken, gratulieren, the possessive takes the dative ending:

• masculine and neuter: -em, as in meinem, seinem, unserem (mit meinem Bruder = with my brother)
• feminine: -er, as in meiner, ihrer, unserer (bei ihrer Tante = at her aunt's)
• plural: -en, as in meinen, euren, and the noun also adds -n unless it already ends in -n or -s: mit meinen Freunden (with my friends), bei meinen Eltern

As in the accusative, euer loses its second e before an ending: eurem, eurer, euren. Remember that es geht also takes the dative: Wie geht es deinem Vater? (How is your father?)