Yes, indeed the verse is a little tricky to parse, and I agree with both of you, it would be better to construe it in such a way as to make the intent clearer.
Ven Amatabhani’s point is well taken: it is quite common in verse for the parts of a sentence to be out of conventional order, and for repeated phrases to be omitted. Indeed, the commentary supports this, at least in the case of the service for parents:
Idaṃ mātāpituupaṭṭhānaṃ sabbhi upaññātanti evamettha attho daṭṭhabbo.
“This service for parents is recommended by the virtuous”: that is how it should be interpreted.
But I’m still not entirely sure of the intent.
First the grammatical basics. In Sabbhi dānaṃ upaññattaṃ, upaññattaṃ is past participle (“is recommended”), dāna is neuter, presumably nominative. That means that it is a passive construction, with sabbhi read as instrumental (comm. is silent, but it reads sappurisa and paṇḍita as instrumental): “Giving is recommended by the virtuous”.
Now, let us assume that the words sabbhi upaññattaṃ should be distributed across the three lines. The problem is that santānaṃ brahmacārinaṃ (dative/genitive plural) is tacked on at the end, and it is possible to construe them with any of the three cases.
Santānaṃ brahmacārinaṃ dānaṃ sabbhi upaññattaṃ
Giving to peaceful spiritual practitioners is recommended by the virtuous
Santānaṃ brahmacārinaṃ ahiṃsā saṃyamo damo sabbhi upaññattaṃ
For peaceful spiritual practitioners, harmlessness, restraint, and self-control are recommended by the virtuous.
Mātāpitu santānaṃ brahmacārinaṃ upaṭṭhānaṃ sabbhi upaññattaṃ
Taking care of parents and peaceful spiritual practitioners is recommended by the virtuous
It seems to me that all these make sense both grammatically and doctrinally. Ven Bodhi (note 404 in Numerical Discourses) suggests that either case one or three would work, but it seems to me that case 2 works at least as well. Let us consider each case.
In the first case, the main text just says “generosity”, while the interpretation specifies it is generosity to renunciants. This is possible, but it does rather restrict the meaning. Note that the Chinese parallel at EA2 47 has 自知 有布施, which is the same as the first line of the Pali, i.e. the Chinese translator did not specify that dāna applied only to renunciants. Atthakatha and Tika are silent on this point.
In the second case, the inclusion of santānaṃ brahmacārinaṃ obviates the need for the implied pabbajjā in this line, which is good. It does shift the sense slightly, though, as the prose is saying that pabbajjā itself is good, while the verse is recommending good practices for a renunciant.
Finally, in the third case, there are a number of features that link mātāpitu and santānaṃ brahmacārinaṃ: they are in dative/genitive; they are on adjacent lines; and service to both parties is commended elsewhere in the suttas. None of these definitively connect the two phrases, but there does seem to be an affinity.
What do you think? I am currently inclined to more or less keep my original reading, perhaps tweaking it for clarity:
Giving is commended by the virtuous,
as are harmlessness, restraint, and taming,
and also looking after your parents
and peaceful spiritual practitioners.