Are these (in desc) browser extensions safe? and are there any safe, free opensource vpn extension for the browser?

I'm going to assume you're using Firefox based on the 5th extension you mentioned.

As for the adblockers, I wouldn't install multiple as they can conflict with each other and cause issues. I and many other people use uBlock Origin as it is very customizable and you can add your own filters and blocklists to essentially block anything you want. I'm not sure if it works with YouTube though, as I use Invidious.

As for the others, I've used YTNS, CAD and Search by Image previously without any issues. I've never heard of the rest though.

For a free VPN, the only one I'd trust is ProtonVPN. Most others are either running some sort of scam, or are very unreliable. Their Firefox add-on is terrible however, and requires that you are subscribed to a paid tier, so you'd have to set it up in a different way.

If you're ever concerned about the privacy/security of a piece of open source software, there are tools available that can scan through the source code and check for tracking or malware. One of the great things about open source is that, if you know what you're doing, you can modify the source code yourself to suit your own needs.

Edit: Fixed broken links (I hope)