I have a similar timeline as you; I called the CIC Call Centre this morning for very similar questions, as it was already passing the "20-24 months" timeline. The "in process" date most likely was when they started to evaluate the sponsorship eligibility. It has been "in process" for just about a month for me now, and the call centre agent advised me that it would take about two months for me to get the sponsorship approval, but it could get even faster as more CIC employees now are back to work. The agent further addressed that after that, the Sponsorship Approval letter (SA, or Decision Made #1 / DM1) would be sent both electronically and via mail to both us and our parents. After the SA/DM1, the file would then be transferred to each local office. The rest of the process would then start concerning the applicants, i.e. our parents, for their background checks, medical exams, etc. The agent that answered my call today was very friendly and forthcoming, but understandably that he could only reveal what was already there.
Since submitting my application in 2019-6, it went quiet for just more than a year, until the AOR arrived in 2020-9. Ever since then, it has been quiet again, until the recent "in process" notion seen on ECAS. The PGP programme, particularly if parents are currently not in Canada, likely has the lowest priority. There is not much we can do other than waiting for the approvals.
Best wishes.