Failure or generic disguises lead to suspicion. The guards ask questions. A success on deception, persuasion or the forgery here means the characters are waved through. The guards are satisfied by the explanation enough that the paperwork is irrelevant, or they're show the paperwork first and it comes out good.
Paperwork is bad? Try to talk your way through. Deception check bad? Show them the paperwork!
A failure on both leads to the guards investigating the wagon, at which point we're looking at a group stealth check, probably with advantage, because the hiding places were established up front and some care taken.
Success on that one might still lead to the players being denied access... but maybe it just leads to the guards taking the wagon up to the house themselves! Failure here is probably the trigger for combat, depending on whom is found. Most likely though, the guards are not keen to pick a fight, because fighting means dying. Dying for money isn't a guard's job, and nor is arresting criminals. So they'll withdraw, tell the characters to wait while they get permission from the house, and contact the city watch/guild heavies/angels of justice. Or maybe the wagon gets directed to wait in the on-site wagon crushing machine.
All in all, the characters are now likely to succeed at their plan. Instead of having to succeed 4 checks, which has a 31% chance, even if each check has a 75% chance of success, they now need to succeed at 1. Tension will be heightened with each failed check as they get deeper into it, and finally: They can try another plan even if they completely fail!