25 Mbit/s is fine for streaming one 4K UHD video with surround sound.
It is mainly just large downloads where speed matters. Downloading a new game, or a big update to a game you have, or a major OS upgrade, will usually take longer on a slower connection. (Not always, because the server might not be fast enough. Not everyone pays the bandwidth costs to allow their download servers to support a bazillion simultaneous gigabit/s downloads).
When I dropped cable TV/phone and went internet only, I decided to cut my speed from 600 Mbit/s ($90/month plan) to 100 Mbit/s ($55/month) to see if it was good enough. (If not, it could be raised easily just by placing an order on Comcast's website. No need to even interact with a human--they only make you interact with a human if you are trying to do something that will lower your bill).
That was 6 months ago, and it is still sitting at 100 Mbit/s. I almost never notice that it is slower than it once was. Most large downloads I do are things I download in the background while doing other things, and then get to sometime later. For most of them, all the change from 600 to 100 did was mean that the gap between the download finishing and my getting around to wanting the data is smaller.
One other important consideration is uploading. My old 600 plan had something like 25 Mbit/s upload. My 100 plan only has 7 Mbit/s upload. That sometimes is noticeable, such as when I need to upload a file to a server for work, then ssh to the server to do something there with the file.
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.
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.