Article 18 puts a duty on the RP to appoint one of more CP, and to 'arrange' co-operation between CP's. This is not a duty on the CP so there is nothing in this article that forces a CP to do anything.
From guidance note No. 1:
"It should be noted that the responsible person cannot
devolve their personal responsibilities to a consultant or employee."
Managers etc get specific mention in article 32, and can be held accountable for any offence caused with their knowledge or due to their neglect, regardless of whether the RP is guilty of the same offence.
Article 22 puts a duty on RP's only, where there is more than one RP. Article 22 cannot be used for the employer/manager scenario as the manager cannot be the RP since we have an employer fulfilling the role of RP and the inability of an employer to devolve their responsibility. (Saying "owner/manager" is muddying the waters, because if the owner employs a manager then they are clearly an employer, apart from the case of where a building owner employs a managing agent. The managing agent scenario is dealt with under articles 5(3)/5(4).)
Therefore, IMO, the need for the manager to co-operate with the employer comes firmly under article 23.
Article 23 puts a duty on employees only and I agree that we could not serve a notice on an employer regarding this article. It would be rather hard to serve a notice on an employee too, as an enforcement notice has to have a finish date, so we would essentially be saying that you only need to cooperate until such-and-such a date. This article is more use if used simply to point towards where an employee is creating an offence by their behaviour.
Also, why would we need a specific duty for the RP to cooperate with employees? The RP has all its general duties regarding fire safety covered adequately by articles 8-22 of The Order. The Order tells the RP what to do, the RP tells the employee what to do. Simples?