OK, presuming you have internet access on your tablet, you could search for these apps in the market and install them:
Aldiko
Laputa
Acrobat Reader
Also presuming you have an account at where you bought the ebooks, so log into that account using the FT3 and again, download them to save onto the tablet.
Now you should be able to use one of the earlier apps
Aldiko
Laputa
Acrobat Reader
and find your ebooks you downloaded and read them.
You just have to find the way that suits you, your Father-in-laws tablet and how he wishes to read them using the software suggested, or other suitable software.
It's daunting to start with, but we will get there, just do not panic.
You could ofc download all the ebooks to your PC, copy them to a suitable SD Card, in a folder called ebooks perhaps?, and use the software to read them off the sd card, or use a file manager to copy them again from the sd card to internal FT3 storage, and then use the software to read them from there, but 1 step at a time eh?