Moving through object: it depends.
I (mis-used) related rules for a chase through a busy marketplace based on overland travel/difficult terrain - halving movement speed for passing through obstacles (aka heavy terrain):
My players saw a pickpocket-spiel in a marketplace - the thiefs did the ususal 3 on 1: 1 runs into the mark and is apolegetic about it, helping it back up and patting them down, etc. Another pickpockets the mark while it is beign fussed over by the first and passes the object to a third which casually walks away.
Normally the marketplace is a big open place with a few fixed stalls (smithy, butcher, ...) for everyday-sales. On market day though plenty of smaller tents, carts & carriages as well as arrangements of baskets/boxes with goods in them are stuffed between the fixed stalls - only small alleys are left.
Players were warned about pickpockets, keeping track of their surroundings while equipping for a travel ahead. They picked up on what some thiefs did, detected the object-pass and two of them gave chase while the others tried to "arrest" the bumper and the actual pickpocket which quickly escalated into a brawl.
I opted to ignore other shoppers (thiefs and players needed to pass by them) and borrrowed/simplified from special movement:
Staying in the alleys was normal movement, passing through occupied spaces (basket/boxes, carts/carriages, tents) took 100% movement penalty (5->10).
The fleeing thief mostly used alleys and the fixed stalls/tents to try to break sight and get lost.
However, the players started moving through occupied fields and had options to avoid the doubling of movement costs:
- baskets/boxes could be passed through or vaulted over (Acrobatics/Dex: passing through, Athletics/Str: jump)
- carts/carriages could only be vaulted (Athletics/Str: jump)
Missing a dex check just meant it cost the original 10 movement to pass, missing a jump cost another 5 movement on top (15 instead of 10) to get back up.
It was quite a bit of dice rolling (due to the time constraints) - eventually they caught up and arrested the thief.
For a non-time constraint situation I would simply double the movement costs and be done with it.
Similar movement impeding effects (terrain wise) are applied through spells, namely:
which could also give you some help about how to rule it.