Question

they never carry the tune

Answer 1

اون ها هیچ وقت با ما هم نظر(هم عقیده- موافق) نیستند.

Answer 2

ناتوان بودن از خواندن یک ملودی ساده

Fig. [to be] unable to  a simple melody; lacking musical ability.

 I wish that Tom wouldn't try to sing. He can't carry a tune. I don't know why Mary's in the choir. She can't carry a tune in a bushel basket. Joe likes to sing in the shower, though he can't carry a tune in a bucket. I'd try to hum the song for you, but I can't carry a tune in a paper sack. 

reference:www.idioms.thefreedictionary.com/can't+carry+a+tune