Your party members in Baldur's Gate 3 make or break your entire game to an extreme degree. Making sure your party compliments your style is very important, but you might find yourself in occasional fights where your entire party isn't with you. This is because, as with several games like it, Baldur's Gate 3 has an issue where your Companions refuse to follow you.
How To Fix Companions Not Following You In Baldur's Gate 3
Sometimes companions will get stuck on pieces of scenery in the world and you may not realise until too late. The best way to fix this is to switch to the character and manually get them away from the piece of scenery that they're stuck on, and then switch back to your character. If done correctly the companion should converge on your location.
You can also try using the fast travel function, as this should force all of your party members to group up and converge. However, sometimes this won't work if a certain member of your party is a long way from your current party. What we'd recommend in this case is to just do the above method then fast travel as the character to as close to your party as possible.