Even if you could do it, the thing about a discount is it is illusory. Say you work out the budget for the year and it is $10,000, i.e. you need $10,000 to meet expenses etc. So you have to raise $10,000 in levies. If you set that budget and everyone gets a 10% discount then you will only raise $9000 and you will have a $1000 shortfall.
Therefore if there is a discount available you factor that into the budget, which you then have to set at a higher figure.
Going back to your friends’ issues, in the case of the one where the other 11 owners don’t attend/vote at meetings, perhaps the best option is for your friend to apply for appointment of a compulsory strata manager, on the grounds that the OC isn’t meeting its section 62 obligations.
Your other friend may also have that option, depending on the state of the building.