Hey
You *could* try https://www.netlimiter.com/ and see if that works.
What speeds are you connected at? ADSL or NBN, because that's also going to be a factor if you are only getting 5MB/s for instance, then too many devicesare going to cause issues.
Is your smartTV WiFi Connected? I'd go Ethernet and see if that works, or do what my mate does - Stop the kids playing Steam games that download a heap,if that's causing it