If three radiologists who worked together all agreed on an image being benign, is that good? would they lie just to agree?

Biopsy: Assuming you are talking about a breast biopsy, i would certainly feel comforted if three radiologists independently felt that the imaging results suggested a benign diagnosis. I do not think that doctors would intentionally lie to feign the appearance of consensus.

Benign: There is no reason for radiologists to lie about something being benign appearing. If you want you can always ask for another opinion from a radiologist at a different office by requesting the films but from what you describe i think you will get the same answer.