Non-disclosure of "convictions" in citizenship application

This concerns a relative, and I am asking for hints regarding consequences. I am also asking the experienced people here for advice on a personal level because I am desperate and really lost:

The applicant (in his early 30s) signed a paper application for NZ citizenship that was filled in - in handwriting - by his mother who applied at the same time for herself (-> two applications for two persons but one handwriting). The applicant signed the application himself and that is about his only (but decisive) contribution. The applicant is being treated for mental health problems and his mother is his WINZ agent and therefore does a lot of his paperwork. The entire process was prepared and conducted by the mother including sending both their paper applications in one and the same courier envelope.

The mother ticked "no" when it came to the question regarding prior convictions, although she very well knew that the applicant had been in court twice within a short time span around seven years ago. She actually attended one of the two proceedings. I myself would have mentioned the convictions of course, although there might be a possibility that he was not legally convicted (discharged without conviction in one case and the second case was at least initially dealt with as an infringement case).

I heard of this citizenship application only in the 3rd quarter 2021 and - for an important reason other than the "convictions" - had him withdraw this application right away. He received a confirmation from the DIA that they forwarded the letter to the respective team.

The DIA has now contacted the applicant asking him to give a statutory declaration, 2 support letters from members of the community and to explain why he did not mention the convictions. The mother would like to send the DIA a "statutory declaration" on her behalf that she did not know about the applicant's convictions (...) trying to wash her hands and keep her own application untarnished, and she might have done so already, thinking she would be in the know.

I am not concerned regarding the current application since it was meant to be withdrawn and should have been dealt with accordingly by the DIA (they still seem to want to process the application). My concern is regarding possible legal consequences for the applicant in general. Furthermore, he might want to apply again in some years, should the reason for the earlier withdrawal cease to exist.

I am somewhat tempted to write a letter to the DIA (or just ring) and explain the whole situation to them in an attempt to take as much trouble off the applicant as a can. I realize though that there would be some other unrighteous motives too. Ultimately, I do not really want to get his mother into trouble although I am really angry and feel that this would be something that might teach her a lesson needed for a long time.

The applicant differentiates very well, is really pissed off but also loves and sadly needs his mother. I will end this here now before I get referred to some psychology or psychiatry forum ...

Please, any hints regarding the legal consequences and what to do and possibly how to approach it?

Unless one of the LIAs has anything to comment, I'm sorry, but I don't believe there is anyone regularly on the forum who is qualified to advise you. In your place, I would suggest that your relative needs to consult an immigration lawyer. One point is that it sounds as though at the moment your relative counts as competent to run his own affairs, with his mother's assistance (however misguided she may be at times) if he needs it, so I doubt the authorities could accept any input from you, whereas a lawyer could speak on his behalf if it seemed necessary.

Thank you JandM, I appreciate your reply - in particular the point that the authorities would not accept input from me. I am confident that I have now found a promising path to proceed.