After concluding his lamenting he is saying that
aho bata mahat pāpaṁ
kartuṁ vyavasitā vayam
hantuṁ sva-janam udyatāḥ
Word for word:
aho — alas; bata — how strange it is; mahat — great; pāpam — sins; kartum — to perform; vyavasitāḥ — have decided; vayam — we; yat — because; rājya-sukha-lobhena — driven by greed for royal happiness; hantum — to kill; sva-janam — kinsmen; udyatāḥ — trying.
Alas, how strange it is that we are preparing to commit greatly sinful acts. Driven by the desire to enjoy royal happiness, we are intent on killing our own kinsmen.
aho bata mahat pāpaṁ, Oh what a great sin we are committing he is lamenting aho bata, Alas, how strange, how sad it is, kartuṁ vyavasitā vayam, we have resolved to do now vyavasitā, we have decided and why we are doing this? yad rājya-sukha-lobhena, out of the greed for Raja-Sukha, so he is saying just as the Duryodhana was blinded similarly we are also blinded hantuṁ sva-janam udyatāḥ, we have decided to kill our sva-janah, see how many time Arjuna is using the word sva-janah, earlier it was Dhritarashtra Durbhuddhe now it has become sva-janah so the whole conception and frame of thinking has changed and what has caused the change it is the attachment, it is the bodily conception it is the material conception.