Do you think that's a guy with his mom or maybe they're a couple?
ーI wonder if they are mother and son.
「親子かな？」
I wonder if... で「…だろうか」
この場合は mother and son を使って言うのが一般的です。
ーDo you think that's a guy with his mom or maybe they're a couple?
「あの男性は母親といるんだと思う、それともカップルだと思う？」
a guy with his mom を使っても言えます。
ご参考まで！
カナダ 
