Can you use Aid action (aiding during the whole ritual) on Ritual checks? That's basically the question.
I've recently noticed that casting rituals is actually ridiculously hard even for a character perfectly equipped to cast them. Very hard DC for a level that’s twice the ritual’s spell level usually means that a character with the highest available proficiency, a biggest available item bonus, and maxed out relevant stat is still more likely to fail on the primary check than to succeed on it, and secondary casters, even optimized ones, often make things worse. You can mitigate that, taking Ritualist archetype and gaining +2 circumstance bonus to primary checks, and also convincing an Alchemist to supply you with skill-boosting mutagens of 11+ level while you cast rituals in a hour thanks to Speedy Rituals (which means that even this strategy only becomes available at 14th level, and only for 1-day casting time rituals). Allowing Aid to work on Ritual checks would allow for another slight bonus; disallowing it would leave them brutally difficult.
Also, are there any spells that give status bonus to skill checks and last for an hour or longer? I don't think there are any.
Aid another and secondary casters and the ritualist trait all give circumstance bonuses, so they wouldn't stack anyways.
Rituals are very hard to cast and secondary casters aren't there to help, they're feeble impediments that check a checkbox on the necessary things for your glorious ritual and you as the primary caster have to carry their sorry asses.
It's homeruled and such but if you're in a temple of a deity that specialises in that kind of ritual or who's divine skill was the one in the ritual I'd maybe allow a status bonus as a gm?
In my kingmaker Kingdom rules I have buildings that give item bonuses to ritual checks (cathedral to religion, occult colleges to occultism etc)