Withdrawing parent's GC

[purnik]

I had filed my parents GC - concurrent filing in July'2022. Their fingerprinting/biometrics was completed in mid August.
As of 11/01/2022, I-130 shows 4 weeks and 6months processing times for my dad and mom respectively.
Whereas the advance parole i-131 shows 12 months and 485 (filed office-Minneapolis) shows 26 months.

This seems like a very long wait and hence they have decided to return back to India by 25th Nov before the i-94 expires and legally withdraw the application

1. What is the process to withdraw the application?
2. Do we need to withdraw all (I-130, I-864, I-485, I-131) ?
3. Does this impact their existing visitor visa? Is it nullified because of GC application and filing of 485?
4. Does GC/approval of 485 really take that long even for immediate relative(as there is no limit on visa numbers)?