Am i overreacting or do i have a right to feel like this?

Well my mom married my step-dad about 7/8 years ago and so i got 2 stepsisters and a stepbrother. Before my mom remarried, my mom, sister, brother and i were living with my grandparents on our farm, we were healthy, active, happy and we had a little money to spend here and there, but after she remarried we moved to the city and lived with my step-dad and his 3 kids, away from the farm and our beloved grandparents (until they moved to the city and lived 10 minutes away driving time after 4ish years). We started to become less active because mom didn't have enough time to run around with us, we started getting bad habits like eating unhealthy things and sitting about more from our steps and we started gaining weight. Our happiness started to fade and our manners dimmed a little bit because of how our steps treated us. Bascially my steps didnt have good parents examples ie: their dad was always working to get them by, their mom was running about having sex behind their dad's back, their mom wore slutty clothes and smoked, they didnt care about school or their health, so they grew up with bad manners, they stole from my mom, borther, sister and me (cash, jewelry, anything worth money), they smoke, they lie, they talk about us behind our backs, and they insult us. They make us do all the work, and their dad always favors them but my mom doesnt show favoritism (even though she tells my grandparents, sister, brother and me that she doesnt like them because of how they treated us). They wear too tight of clothing, they stink as all get out from the cats and dog pee from they mom's, they bring over lice occiasonally and other illnesses. The torture they do to us gets worse whenever we get our grades back because they get Ds or Fs and rarely Cs and we get As and Bs but mostly As and we are in a higher class than they are (Scholarship rather than general classes). There is a going away party for their 90/91 year old great aunt (she is moving in with her son who lives in a different state) that is this saturday and they are choosing to go to a theme park instead of going and saying bye, when i am still going (i might be a little late though) to the party and she isnt techinally my great aunt (only by my mom's marriage) and i have a party to go to for my great aunt's 90th bday (dad's side)that is in another state and i wont be able to go home in between probably even my grandparents are trying to make it to the going away party even though they arent related at all but they are friends with her. Is it right for me to feel like they are rude, bad manners, insulting, evil and mistreating us and their great aunt or am i just overreacting?