You can check out the full quote below.
Furthermore, Nomura discusses the reasoning behind multiple party members at once, confirming that this will be the replacement of D-Link from Kingdom Hearts Birth by Sleep. You can check out the quote below.
"So it would be tough to introduce many, multiple playable characters, but there is an intention of adding a playable character aside from Sora. Unfortunately we’re not able to disclose who it is yet, but there will be [another playable character]."
"D-Link, that has been done away with. It was actually a compromise in a previous iteration because we were not able to display multiple characters on that platform in that game. We’re able to depict multiple characters. Up to five people can join, even more, multiple characters can join your party."
Click here to view the article