Happy to help!
1) "Pulling some strings" for someone means doing them a favor to get them something. Basically, you are using some special authority or privilege you have to help someone else. For example, if I worked in a bank, and my friend also wanted a job there, I might "pull some strings" with my manager to make sure that the bank saw her resume/cv and considered her specially for the job.
2) "Can't get a word in edgeways" means that you aren't allowed to speak, or you keep being interrupted by others. Ex: "I tried to be a part of the conversation, but my sisters were so excited about the news that I couldn't get a word in edgeways." This phrase can also be written "word in edgewise."
3) There are actually two idioms in your last sentence, so I'll explain them both just in case! The first one is "fed up," and it just means you are angry with something to the point of giving up on it. The second one is "rat race," and that is a term used to describe how people treat each other while looking for money or success. It's a very negative term, and it basically indicates that people will hurt each other in order to achieve their own individual goals.