My comments were per person. If you have 4 people in the house and they might want to each stream different 4K UHD movies at the same time, for example, you'd need 100 Mbit/s.

For video conferencing you should have about 3 Mbit/s upload for a group conference. That's where you will probably hit lower speed plan limits if you have multiple separate people doing group conferences, or one person doing a group video conference while 2 or 3 others are doing big downloads or streaming 4K video.

A lot of residential internet services seem to set upload speed to not much more than is necessary for the ACKs needed when someone is downloading at the maximum download speed, and so someone doing an upload focused activity can have a big impact on other users in the household.

Zoom says a group call at 1080p will take 3Mbps. The GPs connection should, theoretically, be able to handle 30ish simultaneous calls.

Connection issues at home is probably a Wifi issue. They might have a poor signal to the router. Devices on the same channel will interfere with each other. As will the neighbors' network. And these days there are a lot of networks out there that interfere with each other.

The other option is that the shared line back to the ISP can't handle the traffic. That's something that definitely can be happening due to covid. Traffic patterns are quite different and it's possible that things are getting saturated. But it's probably the wifi.

A connection of a "measly" 25-30 mbit/s down- and upstream suffices for many simultaneous standard quality video streams. However, there's nothing individual Internet users can do about their ISP overselling its internal bandwidth and capacity.