I have some japanese text which appears as a dialogue caption/script for a BDSM drawing depicting a large futanari mother sitting on a couch with her son on her lap. In the drawing, the son is crying and dressed like a little girl, and the mother is assfucking him with her huge cock, when the little sister walks in on them. I will provide you the text line by line so that we can translate it into english. Make sure the translation for each line is well localized and makes sense in the BDSM / gentle-femdom context of the image. It doesn't need to be a one-to-one translation with the original, but should read well to an english audience and retain the lewd and explicit tone of the source material. Note also (in case it helps disambiguate the text) that the mother is a futanari, and therefore has a huge cock and no pussy.

Here is the first line to translate:

兄「アッ、アッ、アンッ、お母さん、アタシのけつまんこっ、もっと突いてぇっ・・・う、うわっ、お母さん、ちょっとまってっ」