I am sure this has been asked already, as this is probably a very common problem, but I didn't find anything.
I am playing in a campaign I made myself using homebrewed rules based on a German pen-and-paper RPG called Das Schwarze Auge (DSA; The Dark Eye in English).
I have a problem with a few of my players who tend to get very creative, but take a lot of time while the rest of the group can't do anything.
- Once there was a cook who spent hours running from shop to shop haggling with vendors to buy supplies for the group. At first this was tolerable, because everyone had something to do (supplies to buy, armor to repair), but he kept running to each baker, fisherman, butcher, herbalist etc in each town/village to look for rare ingredients for his delicious meals and was taking a considerable time haggling.
- Once I had an assassin, who tried to kill a few NPCs he didn't like while the group was on a ship. He took quite some time to sneak around, prepare traps, check for any witnesses and kill these guys without anyone noticing him while noone else could do anything as they were sleeping.
- Once my group was exploring an old villa and they lifted the smallest of them on the second floor through a hole in the floor. He then proceeded to explore everything in detail, but the rest was standing beneath the hole waiting for his return, which took quite some time.
I don't want to restrict the actions of these players, as they are often the most dedicated ones and roleplay every of their moves and are often the most fun to interact with as the DM, but the rest of the group often gets bored and frustrated, because they can't do anything. In most of these situations I could neither ask the players to do this between sessions nor could I find anything meaningful to occupy the rest of the group in the meantime.
How can I find a fair balance without restricting these players too much?