I'm not sure what you mean by "Facebook
apps" (plural), or "can't install."
Does it not appear in Play store?
Does it appear but flagged as not compatible with your device?
Does the download fail?
Does download succeed but errors out during the final install?
etc., etc.
More info is needed.
I can think of only one reason why the Facebook app inself would fail to install. That is, if it is/was already installed and not removed properly or completely. If this is your problem, start by going into
Settings>
Manage apps and see if Facebook is disabled. If so, re-enable it and reboot. At this point, it should be visible in the app drawer, and you can either use it or update it.
If you still need help, make another guest post or
register as a member.