I have done some reading on the KX-TD1232 system, but have some problems I can't seem to figure out.

The problem I have, is when someone calls in to the school, all the phones ring. How do I set it up so that only the office phones ring? And is there a way to block the rest of the phones from getting an outside line? (Maybe flexible CO, or Remote Lockout)

Everything is possible on this System.
What kind of line do you use, DDI or analog???
In the CO Parameters you can restriced outside lines.

The lines coming in are analog.

look in flexible day ringing assignments with programming software
untick what phones you do not want to ring!!

I'm not using the programming software. I am using the Manager extension. Is there a way to do it from in there?

Also, what if I don't want those phones to even reach the outside? Like if those phones are only for internal communication? Is there a way to turn off incoming outside calls?

Make a list of what you want and call a Dealer/Tech and it will be done in 1 or 2 hours.

Or read the programming and Features manuals.

Yes you can program from the phone, but you will have to thoroughly read both manuals first.

Yes

Yes