1) I recently heard that one is able to use a wi-fi router to bridge together a laptop or tablet to a printer. What I mean is, is that you take a wi-fi router that it plugged into the wall but does not have a Ethernet cable plugged into it. The "internet-free" router is then used as a bridge to pair a laptop or tablet to a printer. No internet or wireless connection is involved, its just a bridge used to link them up.
So by LAN? meaning with a Cat 5 cable.? If that is the case then all you need to do is plug one end of a Cat5 cable into your device and the other end into the Printer.
If you dont have the distance or right length of cable you can use a Cat5 coupler you can get one here, or see what it is
Here is a guide on Bridge Mode using Cisco Linksys routers
Then here is a guide on setting up Print and File sharing using Bridge mode, for printer etc.
2) My grandfather runs he's own business where he travels all over the central Texas region. He asked me if he would be able to use his smartphone to connect to a wireless printer and he's tablet. Now, I have already figured out that with his new Smartphone, he can no longer use that Hot-Spot feature because of his phone plan. (He is grandfathered into an unlimited data plan from a few years ago and if he were to change plans he would lose the unlimited data which is no longer available for anyone with a smartphone.)
So, Is there a way to connect to the printer via Bluetooth or Wi-Fi direct. And connect his tablet so that he can go on the internet with it?
Do you mean at the same location? Or do you mean is there a way he can use his smart phone like a router and get on the internet and print files from his tablet? That is called ad-hoc mode and depending on the phone and service provider that can work or not work.
Most printers now days offer a App that allows for wireless printing to printers. Just search by brand of printer in the App store for his phone.
Connecting to a printer via bluetooth can be done, assuming the printer and tablet both support it and have bluetooth enabled, and present.
Here is a guide by Microsoft on it.
But, the tablet and printer must be able to do it.
Now, I think for the last part you are asking if he can, by using his phone connected to his tablet, connect to the internet and print to a remote printer, without Hotspot?
Can he tether his phone to his tablet? This is the process of taking the charging cable, that has a USB on one end, and connecting it to the tablet and to the phone.
Here is a guide from PCworld on Tethering a phone and apps that can do it for free.
Overall, you will need some sort of cell service 3G or 4G with data to get to the internet. If you want and can please explain it better and maybe we can give you some more info