Hmmm. I can share with you what I did to convince my wife to let me make a shelf train in my office. Essentially the same problem you're having with your parents 
. I had to convince my wife that it wouldn't be messy, wouldn't be loud (I bent the truth on that one 
) and would look professionally done. Granted, mines a shelf train that's 8 feet up, but the problem you're having is similar to mine. As some had earlier pointed out, come up with a business plan to show your parents you're serious and responsible enough to finish the job. It sounds like your mother is the one that needs the most convincing. Try to prove to her that it's not a toy and will look beautiful once it's completed and that your grandparents and dad will enjoy this layout for years to come as well as yourself. Here's a link to my shelf train you can use as a reference.
https://www.youtube.com/watch?...Ktws1fAuw&t=250s
Good luck!
