The apps are chosen by Android itself, nothing to do with AquaMail.
If you'd already "cleared defaults" for the apps you'd mentioned, then the choices should include all apps capable of handling the respectice file types.
Most likely, you will need a third party image viewer for the TIFF (not the built-in Gallery, which as you've already seen, doesn't come up) and some sort of word processor / viewer for the RTF.