Zoom
Zoom is a great feature rich video conferencing tool and it is compatible on all devices. Teachers can easily create an account by signing in with their Google account.
You must be using a paid version of the software with students. The free version, as with any free software, collects information (e.g. email addresses, IP addresses and more) and can on-sell them to third parties. There is also the risk that if something happens in a Zoom meeting, you are NOT protected by consumer law.
The paid (Enterprise) version of the software is protected by law and details are not on-sold. At last look, the cost of 20 licences in Zoom was roughly $2,500.
If you are looking for more features than the just video, Zoom has many.
Green Screen backgrounds
Chat
Emoji Reactions
Screen sharing
Host can mute one or all users in the chat (this could be a very handy tool)
File Sharing in meeting
Students can use Zoom without creating an account. They will need however to use a meeting ID number and password to access the meeting.
If students are using iPad they will need to access the ZOOM App