His family money, they own a pencil empire. Julia comes from a normal upbringing as far as documented online.
They don't necessarily need to rely on their family money, even influencers with half the size of Julia's following make easily over 6 figures per year, even more if you have your own brand/product.
I work in marketing, and was astonished by the rates. Influencers around 500/700k followers would charge anything between $3k - $5k for a single post, more for stories etc. Imagine how much she's asking + affiliate commission from the gazillion amazon links she's sharing.