In the example you have given you asked why "lives" is used. Yes it is plural and it is correct. The documentary is about multiple people. If it was only about a single person it would be called a 90 minute documentary about the life of an ordinary person. "lives" can be pronounced two separate ways and mean different things so be careful with that.

Sadly there are some people on here that are not professional. I hate to see things like this because it causes others like me who are passionate about helping people to become overlooked. Please report those people to Italki if someone harasses you or tries to do anything other than teach English. Italki is for learning and you should never have to feel uncomfortable.

The term "low key" means to do something subtly. In the example that you gave you used bed wetting. Bed wetting can be embarrassing for a child to deal with so approaching the situation with a low key attitude means that you are going to approach the subject gently and subtly. This term can be used to describe any situation that you want to approach without making a big scene.

Well I have an idea what it means but am not guaranteeing that it is right. A tick is a small insect that bites a person and does not let go easily. You have to pull very hard to remove them. So saying that someone is tight as ticks could mean that they are very close and hard to separate. Hope that helps

you can study books til you are old and grey haired and still not learn english. The best way is to practice speaking and listening. Get on YouTube and search for English lessons and then practice them with a teacher on here. Having conversations with English speakers is the best way to learn