Yes, that about parent I wrote before at https://toolset.com/forums/topic/repeater-fields-groups-in-cred-working/#post-1070131.
However, I can't see how it can works fine (also in general, as 'public form'), for next reasons:
1) MORE THAN UNUSUAL FORM
To get 'parent half' of the form, we ALWAYS first need to use sort of 'trick' to force user to create it. That is not so hard, but in 'real world' there is no such kind of the 'on the fly' forms (so, memberships, intake forms, etc, are different from 'short forms'). In this case, I basically first should to 'force' client to submit his personal data (in essence, to 'register him as user') and just after that to let him to choose the rooms. There is no way how people will accept it. Also if we count that this kind of "collapse' design of form let us to 'trick clients' with "more options"/"check availability" or whatever and to use that 'click' like trigger for 'parent form' submission (as well for collapse".
QUESTION (possible solution)
Is it possible to use 'click' on 'Reserva ahora' like trigger for some kind of automatic generation of 'parent form'?
Than, it could to work.
If it is possible, how to do it?
If you can make it, I know rest of solutions (below).
P.S. - Here is important to mention, that by collapse, button should to check title to "Check Availability" ("Comprobar disponibilidad"), like final submission of form.
P.S. Here is also important to pay attention that by such submission of 'first half' of the form ('form initialization'), field in RFG for 'parent form' (here os Reservas') should to be AUTOMATICALLY SET TO CREATED POST!!!)
2) REPEATER MISSING
Fact is that missing 'repeater' of the RFG.
I think that solution could be one View to get this effect. So, we should to rename button from 'Submit' to 'Add another' and create second action of display of the View of generated 'child form' (RFG reservations set). When user is done, he just click on 'initial button' (parent button), for final form submission.
PROBLEM (how to solve 'removal' of wrong submitted RFG???)
So, if you know how to solve above, it could to work.