Keeping tabs on Mabhouh's movements and contacts would generally need a major surveillance exercise. That means a large team or teams of watchers working in rotation. Particularly in an enclosed location like a hotel reception. There would likely also be a control van, for on-street work, an operational HQ, some specialists, the hit squad etc. 26 would not be over-generous Jane, probably on the light side if Mabhouh had got spooked and made a run for it or went to ground.
Western-backed Syrian rebels say kill foreign Islamic State (Reuters)
from the article: Haaretz probe: Dubai assassins' passport photos were doctored