Converting a Singleplayer game into a Multiplayer game

Hey, we have got another concurrent project. It’s a prototype of a shooter game and we want to convert it to a multiplayer game.

It does not feature any multiplayer functionality as of now.
The scope of the project is very big, I haven’t found all the blueprints yet but I can say the player blueprint is massive.

You may see all of the collapsed nodes, you can imagine in there the average looks like this


(It doesn’t fit my screen)

An animation blueprint that is 5 screens wide and tall.
And many more blueprints for various other objects (enemies, weapons, grenades)

We plan on using the General Movement Component plugin.
But the question is, is this even possible?
And if it is, what timeframe should we estimate to finish it?

I have no prior experience on multiplayer in UE.