Asking the management first
The woman who wanted CWS to speak with the management emailed again this morning. It appears she isn't the caregiver in the area, but is trapping them, she says with the help of a friend. She is now concerned that if they are put back, the cats may be caught.
The main thing to ask is WHY you are trapping and sterilising the cats. If your main aim is to prevent the cats from being caught, then sterilising them first without speaking to the management may mean that you are in for a rude shock. The management may vehemently deny that the cats can stay. If you don't live there, or work there, they have no reason to listen to you. To find this out, after you have sterilised the cats is going to be too late. Plus, even if you remove the cats, this means you save this present lot of cats - what about the others that will move in due to the vacuum effect? There is no way to remove them all.
If your main aim is to stop the cats from reproducing and if you think that in the long run, less cats die anyway, some people continue working in areas with unsupportive management. However, this does mean that every few months, the cats you sterilised may disappear. Most people are unwilling or unable to do this, and that's perfectly understandable.
Given finite resources, time and money, I would actually suggest working in areas with supportive management. It's good to see that the colony is protected, that new cats stop coming in, and that the programme is working. Having the existing cats removed is very disheartening.
So how do you prevent this? Speak to the management as early as possible. You may want to do a few cats first to show you're serious, but the main thing is to outline your programme and see if they are receptive in the first time. If they aren't, consider your options and see if working on another colony may be a better use of your time and effort.