Are there rules for multiple characters working on the same downtime activity besides crafting?

Question

In multiple official materials (Player's Handbook, Dungeon Master's Guide, Xanathar's Guide to Everything), characters are given the option to pursue downtime activites. The DMG and Xanathar's Guide both have multiple activities that allow varying degrees of success (such as Sowing Rumors, Selling a Magic Item, Carousing, etc.).

The only explicit mentions of multiple character working on the same downtime activity seem to appear in the section on nonmagical and magical item crafting in the PHB (p.187)/DMG (p. 129) and the alternate rules laid out in Xanathar's Guide to Everything (p. 128).

Are there any rules (official, playtest, JC tweet, etc.) for multiple characters working on the same downtime activity that is not item crafting?

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For example, consider Crime (Xanathar's page 130), where you are called upon to make three checks: Stealth, Thieves' Tools, and Investigation/Perception/Deception. The number of successes you get determines the result of the criminal enterprise (jailtime, no spoils but escape successfully, some treasure, full treasure).

Is there anything in the rules that allows the two to work together on this same activity (both going on the heist together)? If so, how would this work (the character with the better bonus makes a given check, possibly with advantage, etc.)?

Please support your answer with official sources. This is not an AL session but rules for AL are ok so long as they are official. I am not the full-time DM so it's not simply a matter of house-ruling it.

Answer 1

Note: Credit for assistance with this answer goes to @KorvinStarmast (https://rpg.stackexchange.com/a/114607/36317). Direct quotes from that answer are marked with (*).

This question falls under the purview of the "Working Together" rule. The rule essentially states that when characters work together to accomplish a task, one primary character, i.e. the one who rolls the check(s) for the activity in question, can gain advantage.

Sometimes, two or more characters team up to attempt a task. The character who's leading the effort -- or the one with the highest ability modifier -- can make an ability check with advantage, reflecting the help provided by the other characters. (PHB, p. 175)*

This comes with a caveat.

A character can only provide help if the task is one that he or she could attempt alone. (PHB p. 175)*

In your scenario, the characters "Working Together" on the Crime downtime activity from Xanathar's Guide — making checks for "Stealth, Thieves' Tools, and Investigation/Perception/Deception" — would roll as a group. The character with the highest bonuses (for proficiency and ability scores) would roll each check with advantage on the group's behalf.

I hope this helps!