This question would never elicit a clear answer because no one knows and depends on lot of variables. Now, under the new administration it is anybody's guess about the family based Green Cards. However you may get some idea about the general process / timelines on several immigration related forums on the internet. Search by key word 'Immigration'.
My in-laws got their GC in 7 months since applying last year. For siblings the wait is crazy little over 13 years.
Yes parents come under 1st priority . So it would be 6- 12 months. Sibling come under 4th or last priority as per their category , easily 10+ years. Waiting for priority dates.
Check the monthly visa bulletin issued by the US State Department. It will have the latest information about processing times.