Is it possible to play minecraft with multiple people on the same computer?

Yes it is possible by running 2 minecraft. But the real problem is the active windows or only one keyboards. So it isn't possible. I'm sorry to dissapoint you.

If you have multiple graphics cards, it is theoretically possible to pass through the mouse and keyboard as well as one GPU to the VM, and then set it up as fullscreen on a second monitor. This worked for me in QEMU/KVM on Linux, but on Windows it may be impossible. I used this tutorial on Ubuntu 20.04.

It's possible to play with two keyboards/mouses at once. However, this might be a bit too complicated to install and laggy, plus the way I do it requires a premium software, so I think it would be way easier for you to find a different solution to your predicament. However, this could help out some other people, so here it is.

The tutorial I used for this is here. I didn't get a virus in the process, so it should be safe to use the software. Nevertheless, don't be an idiot and at least be careful. I'm not responsible for anything you do!

1. There's a great multiseat software called ASTER, which you can get here.

ASTER is a paid program: however, it does have a 30 day trial that you could try out, and there are other alternatives listed here that would work out as well. Note that you'll need Windows 10 for the the steps below.

2. You'll need two sets of a keyboard and a mouse, an extra monitor, and you'll probably also need a great PC if your game is very high resolution and has good graphics that will lag you out. If you don't own an extra PC monitor, you can also use a television as your extra monitor. Having another monitor is required for the software. Also, you'll probably need at least half an hour of time on your hands.

3. After you get your materials, plug everything in and make sure that your monitors are connected to the same graphics card. According to the tutorial I used, apparently ASTER crashes your system if you're using a NVIDA graphics card with Geforce Experience, and you have to uninstall Geforce Experience for this. I'm not exactly in the most trustworthy parts of the web currently, but it's your decision whether or not you want to trust them or not. I personally don't use a NVIDA graphics card.

4. Download the installation software. Create a backup in case your computer crashes either using another software or by checking the box in the the bottom left hand corner of the software that says "Create a restore point". After doing this, download ASTER from the installation software by going through the instructions on the installation program, and then restart your computer. After restarting your computer, start up ASTER again, press OK when it asks to update, and then press the correct option for getting a software key.

5. Press on the "Workplaces" tab and set up "Place 1" and "Place 2" by dragging the icons representing hardware for each respective player into the places you want them. If you're not sure what the icons represent, hover over them to see what you're using. For instance, if I want to set my first monitor for me and the second monitor for my friend, I'll drag one monitor into Place 1 and another into Place 2. It's very important that you make sure the icons you're dragging are the pieces of hardware you're using to play.

6. If you get a warning message about sharing monitors, ignore it. There may be more keyboard icons than you actually have keyboards: these are other USB devices that you have connected to your computer. You should make sure that you have the right hardware in the right place by hovering over the icons and checking the hardware names. You wouldn't want to connect your microphone instead of your keyboard!

7. Click apply, and then enable ASTER workplaces on the general setting tabs. Also, change "How to run workplaces" in the settings and change it to manual, so you won't have a problem turning it on/off.

8. Click on "Enable ASTER and Reboot PC". Every time you want to turn ASTER on/off, you'll have to reboot using ASTER.

9. If everything has gone well, your second monitor should've switched on and you can now login and launch your games as if the two monitors were connected to two different computers. When you're done playing, simply press the reboot button on ASTER to switch the two workplaces off. Enjoy :)