You are legally his stepson because he was married to your Mother, and that does not change even though they are now divorced.
(1) I grossed 13k in 5 months, dad grossed 11k in that amount of time.
(2) He grossed 22k all year i grossed 13k in 5 months.
(3) Housing, utilities and everything is split down the middle
# (3) may be true for the 5 months working that you had in common, but not for the entire year. The IRS looks at the entire year.
Unless you provided more than half of your own support for the entire year (which is unlikely, given that you only worked for 5 mos), Dad can claim you and the other boys as his dependents. He files as Head of Household. You file as Single, with no dependents, and indioate on your return that someone else is claiming you.
However, tax year 2017 may be different, so be sure both of you keep good records.
