The mortgage on there could be intentional fraud, by your mom or whoever, or it could be a computer mix up ( human beings don't usually add stuff to those reports manually, it is a bunch of computers relaying any accounts with 3 or more types of matching ID info....if someone has the same name, first and last and age, and any address/town they have lived at, it can connect you and cross your info, especially becasue many accounts don't have an individualizing information, like birthdate or SS# , things like leases/rental contracts, phone bills, utiities etc. I have had 2 instances of another person near my age, from my hometown ( he was actually in my class in High School - her first and last name ( her maiden name, but my married name) are the same as mine, and the computers that compile the credit reports crossed our info and put a bunch of her bad accounts that were in collections onto my report, 2 times, and I got calls from a collection agency, that is how i found out one time and another time I applied for refinancing our home jointly with my husband and the bank alerted me to something that looked wrong on there. Funny thing is, the collection agency called me telling me that i owed my GRANDFATHER (He's the town dentist in our hometown) $900 dollars!?!?! Uhm he doesn't charge me, first of all, and i have not had any dental work in years that would cost that much, just cleanings, since i have no cavities.
It takes some time ( usually they say 3-6 months, but all the times i have disputed anything it has been cleared way faster), but you have to call the credit bureau(s) that has the wrong info on their report and you have to dispute it. They will ask for and find proof that it is wrong and will eventually take it off your report, but you need to keep checking your reports regularly for the rest of your life, to make sure it doesn't keep happening. Like another responeder said, pull each of the 3 reports at least once a year, alternating or rotating which comany you check every 4 months - you legally have to be allowed to get one free report each year from each company.
Also, the answers you were chosing "none" on - they aren't a trick, they are the company verifying that you really are the person whose report it is, you have to answer them correctly, they are questions about what is on your report. But if there is something on your report you don't know about or that is wong, yes, the questions can make it inaccessible online, since you won't know the right answer, and you will have to call or snail-mail them to get your reports.
Good luck and good for you for being pro-active and protecting your credit rating - think how much more damage could be done if you hadn't checked until you needed to buy a house or a car!