"Last week I was at my parents' home."
Translation:Pasintsemajne mi estis ĉe miaj gepatroj.
Ĉe often means "at the home of." It comes from the French word chez which itself comes from latin casa (house). and can be used the same way: Je rentre chez moi / I am going home (literally I am going to my.)
Generally it can be used anywhere you want to say "at" while implying close proximity. Mi sidas ĉe la tablo, mi renkontos vin ĉe la restoracio. But as in this sentence, its meaning can be expanded to "at the home of" (Mi estas ĉe miaj gepatroj)
It seems like Duo Esperanto is giving you sentences in a review that you haven't been exposed to the concept yet. And it seems silly to me to go all the way through the tree and then go back and review. For example I haven't reached the Correlatives verbs or affixes yet, but I'm getting them. Those I'm okay with you can pretty much figure them out. I have no idea how you get "Last week I was at my parents' home. out of the above translation, and I don't know where to look because Duo will only let you see information up to where you are in the tree.