While the buttons being broken won't effect its ability to charge, nor its ability to be opened up, it will (obviously) effect your ability to turn it back on once off.
Now if you are looking to repair the buttons, opening it is not easy per say, but it is possible. I can give you generalized info on how, but without the actual make and model of the device I couldn't be specific.
Here are a couple of videos on how to take Samsung Tablets apart. They should help you get the info you need to open it up.
Samsung Galaxy Tab 2
https/youtu.be/-xT5B8GEEZU Samsung Galaxy Tab 3
https/youtu.be/_UlZnQWQXe4
It would be a very good idea to replace the broken buttons, if you wish to continue using the device. Also, you can, while it is open, remove the outer button cover for the "Power" button, giving you access to the inner (actual pushed) button. You can then see if it will or won't turn on when pushing this. It will tell you if it is just the button that is damaged, or something more.