A few things.
You sound kind of down that your father in law looks down at you. Don’t be. Maybe he can’t help it. He is the father of a daughter and many of these people have the opinion that “No man is good enough for my little girl.”
There is nothing wrong with being a UPS driver. I’m a retired Mechanical Engineer and I’m proud of what I accomplished as an engineer. Years ago I worked in my family’s (four generations) newspaper delivery business and I was proud of my skills as a newspaper carrier.
Last but not least, do what makes you happy. If that’s model trains, so be it. There’s a reason it’s called the greatest hobby on earth.