We are from different ethnic groups or states, and family customs often clash. How can we manage this?

Separate religion from custom: religious matters are held in common, while customs are negotiated with respect for both families.
Allah made people into nations and tribes so they might know one another, and the most honoured is the most God-conscious (al-Hujurat 49:13). Customs that do not conflict with the Shariah are acceptable, but no custom is nobler than another. Common conflicts: wedding arrangements, the language at home, food, child-rearing, the role of a son- or daughter-in-law and how often to visit the home town. Steps: discuss expectations early; teach the children both cultures; do not belittle your spouse's customs in front of family; and face family criticism as a team. Cultural differences can enrich a family if handled with humour and patience. See In-laws.