Here is an even more enlightened overview of the responsibilities at OC in 2007 by the Algarve Resident.
"Resort helps family" http://portugalresident.com/resort-helps-family
The Resident, of course, wasn't quite up to date. The three partners were no longer involved in running the resort because it had been sold. Only Crossland was still involved, employed as Manager of the Ocean Club by Green Trust SA for two years in order to pass on his knowledge. He was in charge of the Ocean Club.
John Hill was in charge of the Mark Warner operation. Mark Warner, like Thomas Cook and Jonathan Markson, had a contract with the Ocean Club to use the facilities.
So although both Green Trust and Mark Warner had the same owners, they had different employees, different areas of responsibility and different management structures. Green Trust, for example, was interested in all the clients using the Ocean Club. Mark Warner primarily in the Mark Warner clients.
After Madeleine's disappearance there was a fine line to tread. Mark Warner continued to offer creche use to the twins, but it was likely to have been Green Trust who responded to customer complaints about the press disruption at the Tapas entrance which culminated in temporary withdrawal of the offer. The solution (by Mark Warner) involved the twins being delivered to MW staff at the 24 hour reception and being taken to the creche by them instead of the parents.
It's possible that these differences didn't help at the time of the disappearance, because there were two sets of employees with different loyalties and priorities. Reception was very much in the hands of the 'old guard'. As such they would be guided by those who had been running the Ocean Club for years; Crossland, Santos, the Batista's.