Y.A. 1980s book about kids pulled into computer game

Question

Trying to remember the name of a book I read in the mid-to-late eighties.

A father brings home an experimental computer game. I remember the game was 8-bit type 2D, may have been level based.

Of the kids, the older brother is somehow pulled into the game, and has to avoid the games monster in order to survive. His younger brother and a friend (friend may be a girl?) try to save him.

At some point they're all in the game, and everything is 2D.

I remember the cover had these blocky-looking black game monsters.

Answer 1

Is the story you're looking for maybe "Space Demons"?

It seems to hit the correct time period, includes getting sucked into the game, having to save people, and avoiding the game's monsters to survive. See below for summary from Wikipedia:

The main four characters in the book are Andrew Hayford, Ben Challis, Elaine Taylor and Mario Ferrone. The plot starts when Andrew's dad brings him an exciting prototype video game from Japan. Andrew, who is a video game enthusiast, shows it to his best friend Ben Challis, who agrees to play the game with him. Later, two other players are introduced to the game: Mario Ferrone and Elaine Taylor. It is later revealed that it is possible to get transported into the game by means of a special gun, which only works when a strong beam of hate is directed at someone. Later on, the four get trapped inside the game and gradually work out the only way to escape and thus win the game is if they conquer their hate.

The cover has the blocky-ish black alien dudes on the cover too. Though they aren't exceptionally prominent.