Can I install iWork '09 and iLife 11 onto OSX 10.9.5

They may work, but I doubt it since Apple did come out with a Mavericks edition. The iLife apps may continue to work except for the two that were dropped - iWeb and iDVD.

I have both iWork 09 and iLife 11 installed on my Mavericks machine; iDVD works (it actually - sort of - still works in Yosemite with a few mishaps here and there). I am also still using iMovie 06 HD and iMovie 09 with Mavericks (iMovie 06 no longer works in Yosemite).

I am also still using Pages and Numbers from iWork 09 as I prefer them to the current app store versions.

Having said all of that, I do not know if the installer for one or both will still work in Mavericks as my copies have been installed since Lion - I've had one software (Final Cut Express) which will run in Mavericks, but has a PowerPC based Installer, so it can't be installed unless you manage to copy every associated/necessary file over. But, it is worth a try. If you want to try it, be aware that if you've installed the app store versions, then it'd be best to uninstall the new versions first or you'll probably get the "a newer version is already installed" message. You can reinstall them later.

Since you obtained it at the app store, it should be listed in your Purchases section (check to make sure) so you can download it again if needed.

Were the apps preloaded or did you have to "accept" them at the app store when you first got the Mac and/or checked the app store?

If they were preloaded, I do not know if you can install older versions as I can't test it because I do not have a machine with them preloaded. They should show in the app store though because you may need to wipe your drive and reinstall. As long as they show, you should be able to download them.

Are you saying that those apps are not listed in your Purchases at the app store? Preloaded or not, you may need to reinstall in case of a problem.