I have managed to update our phones and laptops but can't do our tablets. Having read that norton only works on android 8 or above I checked our tablets. Both are below 8.
Does this mean I can't use bt security at all on them or is there a fix. They are perfectly good tablets so not buying new ones just because by decided to move to norton.
You can not use Norton. Norton have taken the decision only to support Android 8 and above.
Android is now on version 12 which is nearly 6 years advanced from version 7 which was introduced in 2016 and in Android operating systems that is a long time.
Norton have obviously taken the decision not to cater for such an "old" operating system and as BT have decided to go with Norton your only option is to use another AV product or update the tablet's operating system if possible, which you probably won't be able to do because the manufacturer of the tablet will probably have decided not to support the tablet any further with Android updates so you could just as easily blame all three companies.