There was a vlog recently where Jess showed the apartment she lived in when she was young and it was just her and her mom. From the outside, the apartment looked normal, I recall it sat above a restaurant on a busy-ish street. I'm from the US, so I have no idea what the market was like in that particular area of London 20 or so years ago when Jess was young, but it didn't look like anything super nice like what they have now. Also, there was a video maybe a year ago where Jess and Zak went to visit her grandma and they were in the living room I believe and the decor looked very normal for a grandma lol. It wasn't crazy lavish or anything. I'd imagine her mom grew up quite comfortably, but it seems like a lot of her money has come from her current position + her husband's income (and we have no idea what her husband's financial background is either).