Combining data from multiple tables can be a challenge. If the relationship is linear, Grandparent--Parent--Child, you can base your report on the child table and add fields from the related tables as needed, often by putting them in sub summary parts. Things get more difficult if the relationships are not linear and you need lists of records that aren't directly related on the same page.
You have several options.
One is to set them up as separate reports on separate layouts, then save the first report as a PDF, pull up the second report, save it as a PDF, appending it to the end of the first PDF file. You can do this with a script that uses the "Append to existing PDF" option.
Some times you can list records from the third table in a large portal set to slide up, but this has built in limitations that may keep it from being acceptible.
Other approaches may require a different table used just for reporting, you import the data as needed into this "report table" merging records from several different tables and then delete them after the report has been created and printed.
Thanks Phil.. I like putting all data into a file then reporting from that as best choice. I appreciate it!