Online videos will only get you so far.  I'm sure you have read it plenty of times by now, but practice is the best way to go about this.  You need to be able to train yourself to notice big and small mistakes alike and videos most likely will not help you in all cases.  For instance, if you follow a video on something, but come across an unexpected problem not addressed in the video, you would not understand what was going on.

To learn a language purely independently will require a great deal of self-motivation as well though; however, if learning this is what you have your mind set on, then I suppose that would not be an issue.

I would recommend watching videos online. Just to get the basic idea of each language. Please do not limit yourself to just videos I also strongly recommend to check out books from either your public or school library. Chances are these books will be out of date but the basic ideas and concepts are still the same. Once you grasp the basics I recommend you begin to practice...and practice. Something else I have learned is to copy code from other people online and try to understand what is going on in the program. Once you learn, try to manipulate the code to make it do something different.

Here is a list of youtube channels that I follow:

LearnCode.academy (Web Development)

thenewboston (C++, Java, C#, C, Python, PHP, JavaScript, and the list goes on....)

mybringback (Java, Objective C, C, Ajax, JavaScript, Python, and the list goes on...)

These channels provide a playlist for each language. I hope this helps.

Websites like khanacademy and codeacademy helped me. The best thing is to try and see what works for you.