1: Okay, the first one is a case where the lines can only really be understood in the context of the verse as a whole. This is quite common in verse, as the normal word order is not observed. Here is my translation. (I just noticed a mistake in it, so this is a little different from the one on the site now at SN 4.23)
For how, Blessed One, can a disciple of yours,
Kathañhi bhagavā tuyhaṃ,
one who loves your teaching,
Sāvako sāsane rato;
a trainee who hasn’t achieved their heart’s desire,
take his own life, O renowned one?”
Kālaṃ kayirā janesutā”ti.
Note that the opening idiom Kathañhi expresses a sense of outrage or objection, which we might render “How on earth …”
The translation “Have people heard …?” is a mistake.
2: This is a very idiomatic phrase, which I wouldn’t try to render literally. It means “How very fortunate!” “How lucky I am” etc.
3: This is a very difficult line, and I follow Ven Bodhi’s reading. He comments:
In pāda a, I read acchejji with Se, an aorist of chindati, to cut. The finite verb seems to me preferable to the absolutive acchejja of Be and Ee1 & 2; the variant acchecchi suggested by PED may also be acceptable. This verb should be distinguished from acchejja (or acchijja, Ee1) in pāda d, an absolutive of acchindati, to rob, to snatch away. The Be and Ee1 reading of pāda a may have arisen through a confusion of the two forms. I read pāda b: addhā tarissanti bahū ca sattā. Be, Ee2, and SS read the last word as saddhā, but the gloss in Spk supports sattā: addhā aññe pi bahujanā ekamsena tarissanti. The BHT version of Mvu is too different to be of help and may be corrupt, but Jones (at 3:273, n. 4) suggests replacing raktā with sattvā, which would then support the reading I have adopted. Tarissanti is certainly preferable to the v.l. carissanti, found in Be, Se, and Ee1.