Unlike in English, you don't add an -s to surnames in French when talking about a whole family.
The plural of surnames in French
Look at these two cases:
Les Richardson nous ont invités.The Richardsons invited us.
M. et Mme Dupont = Les DupontMr and Mrs Dupont = The Duponts
Notice that surnames in French don't take -s when plural (unlike English).
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