Can I install 2 printers in the same laptop? The model of printers are HP & OKI.?

Sure you can. Why not? You can load as many printers as you want. One will be your default printer so if you want to use the other one you have to specify after you hit the print button.

Yes. Just load the printer drivers and go to control panel > Printers and select which one you want to use each time you need to change. All you have to do from there is right click on the one you want and select "default printer" and close the windows you've opened.

i think the limit , only depends on how many spare USB 2 ports u have.

so, yes, no problem, the app will just ask you which printer or scanner u want to use.