@crinrict Ran two tests. This was interesting.
1. Moved the two guys to a house in Willow Creek which I built. Same issues as originally described, but the second sim never started cooking. His queued action stayed as "Gather For Group Cooking" and, once the cooking was done, the action simply canceled itself. The Zombie Cake, with proper 12 pieces (for having been cooked by two people), was delivered without further incident. To me, this is non-problematic, but it is admittedly and obviously not what is intended.
2. Moved the two guys to a house in Brindleton Bay, Chateau Frise, built and provided by the sims team(s). The second sim joined in the cooking! ... but then (dun dun dun) his actions and activities canceled in the middle of the cooking sequence! His bowl simply disappeared and he stood talking to the other sim. However, the Zombie Cake, with proper 12 pieces, was delivered without further incident. To me, this is close to what is supposed to be happening, but not quite, lol.
If you want to pursue this, I will continue to cooperate. :D