Yes Squawk, Litigation Solicitors and Barristers do!
Cost SHARING is legal and there is no legal requirement for you to sit in the left seat, you could sit in the right hand seat if you wanted to but you would need to check with your CFI, it may require a check ride or be prohibited by the SO's. why bother anyway-pax will be happy in any seats.
Do consider your responsiblity to the pax in regard to safety briefings etc.
I would find another flying school if yours charges £5.00 per pax, like everything shop around, many make no charge