Thanks for your time, that's actually helped me sort out another problem I had.
Although it doesn't really explain why I can respawn on the markers but team mates (in coop game) cannot. We are all on the same side.
However, I seem to have solved it by accident. Deleted one of the markers and replaced it with a new one. The new clear markers are now purple colour and they work for everyone. The previous ones I placed were green colour. I cannot even find those in the markers list any more. I don't know what changed or what the different colours mean for markers but the purple ones are working properly.