If you rent to two individuals seperately, you'll have to pay the council tax (which might be why the rent looks higher online).
The council will bill you regardless of what you agree with the tenants.
If you rent to two people "jointly" that isn't the case, but it's more complicated if one wants to move out and the other doesn't.
The tenants can sort out who's on the bills, but often the arrangement is that it's your name, but the tenants agree to pay the bills.
When I post, I am expressing an opinion - feel free to disagree, I have been wrong before.
Please don't act on my suggestions without checking with a grown-up (ideally some kind of expert).