So I want to remake an old game and I don't know if it's possible to give my remake for free, and I'm planning to copy the assets like sounds and art, so can I give my remake to friends?
If not, can I still make it as a hobby project and privately keep my project?
If the game, assets, etc. do not belong to you (ie. you did not create them yourself without copying from another source, or pay to obtain a licence to those assets), you do not have permission to redistribute them. Not even for free. Not even if you conclude the game is "old" or "abandoned" - if it was made in the last 70 years (which covers all video games), it's still protected by US copyright laws and likely by similar laws in other jurisdictions.
With regard to doing so "privately" - well, if you keep it private, how would a rights-holder or law enforcement know to chase you down? That doesn't necessarily make it legal or ethical - just from a practical standpoint, you might be able to evade consequences as long as what you intended to be private remains so. If the game were to leak outside of your private circle, that could again open you up to legal risks.
If you want to substantially recreate an old game for enjoyment or learning purposes, a safer way to do so is to create an homage. Use the original game as inspiration, but change things to make them your own. Make or source your own art and sound assets that you have licence to use. Experiment with tweaks to the mechanics. Write your own story, etc. Make it your own creative work, even if it borrows heavily from the conceptual structure of the original. This puts you on much better legal footing to share the game, show it off as a portfolio piece, or possibly even sell it.
