Hello again!
In this case no you do not say 'your family are very nice' this is because 'family' is singular 'the family'. You would use are in a sentence when it is more than one. For example. " your siblings are very nice"
Hope this is clear and it helps!
3 สิงหาคม 2015
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Technically 'is very'. Practically - either is fine. People use both.