For group 15 hydrides EH3 (N, P, As, Sb):
Statement A is correct—stability decreases down the group as H-E bond strength decreases.
Statement B is correct—basicity decreases as the central atom becomes less electronegative, making it less willing to share electron pairs.
Statement C is correct—reducing character increases down the group as the hydrides become easier to oxidize.
Statement D is incorrect—boiling points do not consistently increase; NH₃ is anomalously high (-33°C) due to strong hydrogen bonding, but PH₃ (-87°C) is lower, and the trend is irregular.
Therefore, A, B & C only are correct.