You can do it without a mod. Go to %appdata%/StardewValley and open the file called startup_preferences. ctrl + f for "playerLimit" and you'll find something like this: -1.
Change the -1 to any number you like... (e.g. 8). Now you can play with up to that number of people.
Keep in mind every person will need a cabin in order to join. And the mode is slightly experimental, so some things might work a little strangely. The only actual crash I know of is if you try to go to the movie theater with more than 4 people. You have to go in batches of 4 and it will work fine.
Have fun