Exegesis:

kai autoi ērxanto suzētein pros heautous ‘and they began to discuss among themselves.’ kai autoi (not emphatic) indicates the change of subject. For archomai with infinitive cf. on 4.21. Here it refers implicitly to a reaction to the startling communication of Jesus in v. 21.

suzēteō (also 24.15) ‘to discuss,’ ‘to debate.’

to tis ara eiē ex autōn ‘as to who of them might be….’ The indirect question is made into a substantive by prefixing the article to (cf. on 1.62), and this substantive is the object of suzētein. For ara cf. on 1.66. ex autōn stands for the partitive genitive.

ho touto mellōn prassein ‘the one who was to do this.’ mellō with infinitive is somewhat more definite than the simple future.

Translation:

They began to question one another, cf. on “said to one another” in 4.36.

Would do this, or, ‘planned/intended to do thus’ (Bahasa Indonesia).

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.