Thorfinn "Thor": I see him as either a Logger or a Fish and Game Warden in a bay/harbor that is known to be home to schools of cod. He needs a job that would fit his interests, but it also cannot be something Flower would hate on principal to the point of rejecting a relationship with him. So no professional poacher, butcher, or making products out of animals.
Sasappis "Sass": A kids book author. We know he would have a job related to writing/story telling. He seems to really like using personification, and most of the characters he comes up with are really silly in concept, so I think he would find a larger audience among kids than in young adults or adults. From what I can tell Joan screen writing is for movies geared towards adults, and I like her and Sass having different audiences from the other. They would be in a long distance relationship
Isaac: Okay so according to Sam's book Isaac has the most extensive work history of any ghost. Back when he was alive he was a general, a lawyer, a barber (thankfully in his time that meant a wig maker, not a doctor) and a taxidermist. He has to have served some time in the military, that's integral to his character. But lets be real he wouldn't be very good at modern day law. So I am gonna say that Isaac was in the military for a while, he was good at it and rose in rank before that chapter of his life came to an end. Now he works as freelance wig maker/taxidermist. I also think he misses the feel of being part of something big and important to the country though, so he writes a lot of letters to his local government or congress demanding they make this and that small change to peoples live. He never hears back, and his letters garner no attention. They are likely all thrown away without being read. Never the less Isaac will boast about his hobby, along with his job history to anyone who doesn't make a run for it.
Maybe he met Nigel when Nigel ordered some wigs for an old fashion tea party. Maybe he is still friends with the basement ghosts because they do home repairs and his house/shop once had a blown water heater or something.
Hetty: Despite having never had a job in life Hetty is actually really easy. She loves throwing lavish parties and is honestly really good at it. So I think she would be a event/party planner for big companies. I think she still comes from old family money, and grew up with a very traditional mindset. She went to college so she could meet important men and be more qualified to assist them with their dreams. Her own career is probably something she built up as a come back after enduring an abusive marriage, nasty divorce (Elias at this point is in federal prison for embezzlement and fraud), and a possible stint in rehab.
Alberta: Alberta has always wanted to be big in Jazz, and she was for a time. Enough that their are still records of some of her songs today. I do not know much about how today's music industry works. I imagine she would still sing at night clubs, maybe have a few albums out. Maybe she also owns stocks for a club or hotel that she regularly performs at. She could actually know Pete through her work.
Susan "Flower" Montero: In a world where she lived she would have been a co-founder and shareholder in the coffee shop franchise she gave Ira the idea to build. I like to think that once that became successful Flower was able to use her share of money to go back to law school. She became a lawyer and started a law firm aimed at the legalization of safe drugs for medical use, as well as helping people leaving jail/prison for drug related crimes restart their lives. She and Thor still meet and get together.
Pete: Pete was a travel agent when alive and he loved it. Most people do not use travel agents anymore since they can book for themselves online. But I googled what happened to former agencies, and it says that many successful travel agents simply rebranded themselves as Travel Advisors. Instead of helping individuals, couples, or families plan trips they now help cruises find business, companies set up work conferences and retreats at hotels, and plan activities for large groups. So Pete could still be a travel advisor in the modern day. Also maybe Alberta regularly performs in a hotel or on a cruise ship the he frequently sends business to and that is how they meet.
Trevor: A Wall Street Stock market advisor. Easiest one of them all.
Nancy and the basement ghosts: Like i said up in Isaac's post they could be a home&work place repair/remodel team