Actual experience when it comes to hand baggage varies a lot, best is to be compliant with the HV requirements.
Personally on the single HV flight I took people were allowed whatever they want, but experience I heard from friends/colleagues is that in some cases it is more strictly enforced.

For cabin luggage, the MSC rules apply, in case of your GLA-AMS-SOF flight the MSC is KL, and on the return the MSC is HV, your best bet might be to call the local KL handler which seems to be swissport - https://www.glasgowairport.com/desti.../airlines/klm/