Remember that there are some verbs in spanish that have a pronominal form and a reflexive one and the reflexive form sometimes changes the meaning of the verb. Also notice that not everything can be translated literally word by word from one language to another, so, there are some of those verbs that you'll have to learn by heart, that is the bad news, but the good one is that there are not as many as you think.
Talking about the verb quedar/ quedarse both forms have different meanings in spanish and unfotunately you will have to learn that "quedarse" means stay. But is more complicated it's pronominal from since it has more meanings including to stay, to remain, sometimes it can mean "to agree, to leave, to schedule" depending on the context of what you want to convey.
The verb volverse can also mean several thing such as "to become" or "to turn" and both are reflexive forms that cannot be translated into english as such because it wouldn't make sence in english. So, as I said some verbs you'll have to learn them by heart, but there aren't that many so i think you can do it!
Excellent question! I hope I was helpful! Saludos!