and can I delete them without out affecting mine?

Answer:
They use up file space. Since they're not being used, you can delete the accounts through 'User Accounts' in Control Panel.

However, I highly suggest that you use 2 accounts. EVERY home Windows user should have 1 administrator account (for program installing and other system tasks) and 1 regular account for day-to-day work.

The biggest mistake most Windows users make is that they always run their personal with administrator access. This means that any malicious program has the freedom to install trojans & viruses easily.

Answer:
If ur pc has 3 users & only 1 user is logged at a time than total amount of memory wil b available for u only n not b waisted due 2 other users. However u can delete other users if u dont need them.Before doing this just save data from individual users my document folder as it wil get effected.To do this turn of ur pc completely n restart,during booting press F8 key n log as administrator,than go to users in control panel n delete unwanted user accounts.
Answer:
depends on how many files are on the other accounts depends on how much memory they use but you can delete them with no problem they wont affect your account
Answer:
Yes, you can. Make sure nobody needs the files/email on them first thouth.

Each account is independent, you can add/remove accounts at will.

Answer:
yes it does affect your memory because if you have two accounts all the programs in your computer have to get doubled as well so double memory but you’ve three users!!