Be (all) brothers/sisters under the skin phrase
Although two or more people are obviously different in some aspects such as appearances, position, etc., they have similar feelings or thoughts.
They are brothers under the skin, but they seem to not know about it.
My friend and I are sisters under skin, as we both hate spicy food.
The verb "to be" should be conjugated according to its tense.
To quit; to give up, stop doing something because you know that you cannot succeed; admit defeat
The team is not going to throw in the towel just because they lost one game.