Being two “things” at once

Solution 1:

Johannes factotum ("Johnny do-it-all") or less obscure Jack of all Trades.

The first thing that came to mind was

Jack of all trades

It's not obscure, but it's quite old all the same. From Wikipedia:

"Jack of all trades, master of none" is a figure of speech used in reference to a person who has dabbled in many skills, rather than gaining expertise by focusing on one. The shortened version "a jack of all trades" is often a compliment for a person who is good at fixing things, and has a very good broad knowledge.
In 1612, the English-language version of the phrase appeared in the book "Essays and Characters of a Prison" by English writer Geffray Mynshul (Minshull), originally published in 1618, and probably based on the author's experience while held at Gray's Inn, London, when imprisoned for debt.

In the same Wikipedia article they speak of Johannes factotum, which is not used today and I personally had never heard of before. I thought the Shakespeare reference was cute, and if it's obscure you're looking for this might fit the bill.

In Elizabethan English the quasi-New Latin term Johannes factotum ("Johnny do-it-all") was sometimes used, with the same negative connotation that "Jack of all trades" sometimes has today. The term was famously used by Robert Greene in his 1592 booklet Greene's Groats-Worth of Wit, in which he dismissively refers to actor-turned-playwright William Shakespeare with this term, the first published mention of the writer.

Solution 2:

There's a few where they have one boss but are tasked with multiple jobs under that boss to do whatever needs doing.

• Guy/Gal Friday
• Dogsbody
• Gofer (that's a bit more modern)
• Factotum

Some that imply multiple skill sets

• Jack of all trades
• Polymath
• Dilettante

For holding multiple jobs all I can think of is "Moonlighter".