Need a reliable VoIP soulution with video.

Well, it really depends if you are going to set it up by yourself, or you plan to tell your parents to do it.

If you will do the installation, Tox, Ring and maybe Linphone are now very good choices.

If you need to let your parents to do the initial work, forget the above programs and try WebRTC, like, https://meet.jit.si/ or even Firefox Hello.

https://palava.tv/
works well ;-)

but yes do try
http://utox.org/
download the tar from
https://github.com/grayhatter/uTox

Once installed transform the long numbers ID into small url
there's a copy & paste function which allows easy copying of
1234567897898545122333313336544444444

then paste those numbers at

https://toxme.io/
will give

ex:name at domain
& send that over to your parents

they will have to do same thing over at their end
download,decompress & open uTox

There are some good options posted above. I have also tried Jitsi a while back, with account at Ostel, and it worked well, but the setup was a bit complex. Ostel website for a free SIP account: https://ostel.co/

I second Jitsi Meet for a simple solution. It runs in a browser, functions well and is easy to use. I found it to work better than Firefox Hello, too. I only tried the live web instance, but I believe you can also use it on your own server. You need to make a link and share it to start a conversation, which may or may not be feasible for you. I think it may be the best solution for now, though. Website: https://meet.jit.si/

I think the true replacement for Skype and similar programs will come from the secure and decentralized alternatives, prime examples of which are Tox and Ring. They are both similar, but neither is complete and ready for mass adoption. There are people who use them without many problems, though.

Tox is probably more advanced feature-wise. When I used it, it usually worked well, and I liked the UI. What I had my doubts about was the approach of the developers/maintainers towards the project, which seemed quite chaotic. The organization also went through some internal problems, but hopefully those are resolved by now. Tox consists of a core that many clients have been built around by many people. Most of them seem dead now, but the two that kept around are uTox and qTox. Website: https://tox.chat/

Ring is still lacking some features compared to Tox, but the development is led by a company who already has experience with VoIP software development. They seem to take a more serious approach to the development, and have more concrete plans for some of their work. There is an offical client for GNOME and unofficial for KDE, but of course they may be used in any environment. Website: https://ring.cx/

Both Tox and Ring use a long string of characters you need to give the other person to add them/call them. You only need to do that once, but there are efforts to simplify it. Someone people made websites where one may register to assign a name to their Tox addresses. There's been talk about integrating some of those websites into a client, but I don't know how that ended. Ring is now working on implementing searchable profiles directly on their decentralized network, so the feature is expected to come in close future.