12 hours notice is needed to be off sick
Clearly not enforceable, as can be not well enough to work at any time. However, in the same way SSP has a waiting period of 3 days, any enhanced policy of the employer could indicate no pay until 12 hours notice given.
If we are off sick we need to ring round staff and find someone to cover our shift
No, not legal. It is the employers responsibility. It would be actually against the insurance of the employer for you to undertake this work.
If it’s an emergency or sudden sickness we need an doctors note from A & E or the GP or our absence will not be accepted.
Not needed to be off sick, but again is within rights of own policy to pay or not beyond SSP. Just because you need to pay for it makes no difference - its a choice.
If we are suddenly off with a child we will also need a gps note to prove they are ill.
No, not at all. However, you basically only get one day to arrange childcare, beyond this child being ill is no reason not be be at work.
Is this legal?
If you want to be paid beyond SSP, they can set the conditions. For SSP, no it's not.