How do you politely deal with controlling & bossy people?

I especially don't get the cousin bossing you, I would expect her to be more of a mentor, and helpful to you. (she probably thinks she is) Yikes! A few tricks of my own, was to wait for them to finish lecturing, listen completely, then politely state, "I appreciate your opinion, and I'll think about it". OR "Oh that's probably a good idea; I'll have to look into it." and if there's a follow up from Mom or Cuz, "I'm working on it" or "it's in process" or "I'm glad that works for you, but it didn't work for me" or "How do I fit in this equation of MY life?". Stop disclosing too much information, just the vague details, and no one will be able to correct your decisions. Eventually, your family will understand that you are living your life for you, and not for them. Keep in mind, they honestly want what is the best for you. As for your Cuz, you could ask her why she didn't follow her own rules?