"まともに相手すると疲れる"
- It's exhausting to take them seriously.
- You're going to tire yourself out by listening to them seriously.
- You will exhaust yourself by dealing with them.
親の言うことをまともに相手すると疲れるよ。聞き流さないと。
- If you take what your parents say seriously, you will get tired. Pay no attention to what they say.
- You're going to exhaust yourself by seriously listening to what your parents say. Have their words go right out the other ear.
If you take everything your parents say seriously, you'll be exhausted.
If you listen to every last word your parents say, it will tire you out.
この場合、次のように言うと自然な感じで良いかと思います。
ーIf you take everything your parents say seriously, you'll be exhausted.
「親の言うことをまともに相手にすると、疲れるよ」
to take everything your parents say seriously で「親の言うことをまともに相手にする」と言えます。
ーIf you listen to every last word your parents say, it will tire you out.
「親の言うことをまともに相手にすると、疲れるよ」
to listen to every last word your parents say でも「親の言うことをまともに相手にする」を表現できます。
ご参考まで！
アメリカ合衆国 
カナダ 
