It helps to get an understanding of the resistance first. Often we assume general resistance without finding out the specific reasons for resistance and miss out on potentially solvable issues. 5S doesn’t necessarily mean there are signs on the wall. There may be options for more subtle visuals that are in line with their ideas of what the workspace should look like. It might be helpful to start with a digital 5S to establish order on shared drives first.
The success of a more modest 5S could become a “proof-of-concept” that helps you “sell” the idea as a whole. You may also try using the 5S Assessment Tools in order to get the their input as well as the input of others. Then you’ll have a baseline of how easy it is to operate within the work space. I hope that helps!