I mostly run Dnd 5e and i do not have the DMs guide. I find that while it is useful, it is not completely neccessary to run the game. Only the Players handbook and the Monster Manual are for homebrew.

My question is, are there separate core rulebooks for players and for the GM? If so, is the GM version absolutely necessary to run the game? Also, are there any other books that you would define as neccessary such as DnDs Monster manual?

Also, i was recommened to play the "Mongoose 2nd edition version" and an honestly pretty confused because i try googling that and am brought to an amazon page with "traveller MGP40000" rulebook. Please help me be not confused.