Hi Piyush. If Task A is a Parent (or Parent.Parent, etc) of Task B, a Task Report filtering for Task B can also then refer to Task A (eg Parent.Custom Field Of Interest); but if not, then they are indeed unrelated, and instead, I suspect you will have to filter for Task B OR Task A, thereby yeilding "two separate rows, with the two columns of interest" (unless it happens to be the same Column Of Interest on both Tasks you are after).
Regards,
Doug