Thank you, everyone. I spoke with my wife this evening, and she has agreed that we need to separate her aunt and cousins from us. After reading your comments, I realized part of the problem I had was I wasn't being firm enough, but after I got off work we went to get some coffee and talk; just the two of us.
I told her that she was putting her aunt before our family, that she was jeopardizing our daughter's future to help other people, and I couldn't be with someone who would do that. She agreed and said she was just worried about her cousins (I haven't mentioned yet, but they are 3 and 15), and that she didn't want them to be homeless, so we compromised: they can stay with us through the end of our rental agreement in April, but after that they are out. This gives them over 2 months to figure something out, and we were gonna be in our current place until then, so it feels like a fair compromise.
I have already spoken to our landlord and told him we wont be re-upping our agreement, because I don't want it to be April 29th and she still hasn't found some place so we have to let them stay with us even longer. I'm taking a hard line against this without completely pushing my wife out of the way, but if I get the whiff of her trying to snake her way into staying longer, I'm gonna put my foot down and take more drastic measures.
Tomorrow I'm going to speak to my branch manager (we have a one-on-one meeting scheduled) and tell him I need his help to move up. The nearest assistant manager position is almost 80 miles away, and I would only get a small raise despite essentially doing the same work, so I'm gonna shoot for the moon and tell him that he's gotta help me get a branch manager position or I'm switching jobs (I have already applied at two other banks and have a few more to apply to after I post this update).
Sorry if this is rambling or incoherent; I'm doing it all on my phone while my laptop charges and can't track and edit my sentences as well. I feel a lot more confident about the future now. Y'all told me essentially what I already knew, and you helped me find the words I needed to get my point across. Thank you for the messages in my inbox and all the resources and information. :-)
I'm gonna go back to my normal lurker status now; gotta read all the blogs and forum posts so when my time comes, I'm ready as possible.