Marrying via civil marriage is not forbidden; but it lacks some of the conditions that a valid Islamic marriage (nikah) requires, which are:
– Considering the milk kinship as a prohibition to marry
– “Being chaste” as a condition of marriage
– The right of mahr (legal share of bride) for the bride, which is not a prerequisite but a result of the marriage. It must be determined absolutely, and given to the bride.
You can marry with civil marriage and start a family if you regard these conditions, without needing another nikah. Your marriage would be valid, but the legal share of bride, which is the right of mahr, should be guaranteed with another contract you could make.
See the fatwa below for details: