A.T. Robertson Commentary John 8:39

"They answered and said unto him, Our father is Abraham. Jesus saith unto them, If ye were Abraham`s children, ye would do the works of Abraham." — John 8:39 (ASV)

Our father is Abraham (ο πατηρ ημων Αβρααμ εστιν). They saw the implication and tried to counter it by repeating their claim in verse 33 which was true so far as physical descent went as Jesus had admitted (verse 37).

If ye were (ε εστε). Strictly, "if ye are" as ye claim, a condition of the first class assumed to be true.

Ye would do (εποιειτε αν). Read by C L N and a corrector of Aleph while W omits αν. This makes a mixed condition (protasis of the first class, apodosis of the second. See Robertson, Grammar, p. 1022). But B reads ποιειτε like the Sin. Syriac which has to be treated as imperative (so Westcott and Hort).