Apostrophe perplexed

[Anonymous]

I am writing an invitation that says "A party at the Challgren's". Do I need the apostrophe? Thank you for your advice!

[Casiopea]

I am writing an invitation that says "A party at the Challgren's". Do I need the apostrophe? Thank you for your advice!

Last name: Challgren
Invitation: A party at the Challgren's (house). :D

Last name: Challgrens
Invitation: A party at the Challgrens' (house). :D