A number of people baked the same type of cake in a shiur less than what is chayiv in challah. They all come together and put it on the same table. In such a way now there is a shiur now that they would need to take challah because of the din of tziruf sal. However the cake will be taken afterwards by many people as it is being served by a kiddush. Is this called that it was made to be “m’chalek” (separated and giving out) and even though through the fact that it was all put on the table now together, still it’s not chiyuv in taking challah?
Placing the cakes on the table does not necessarily imply their joining together, as the Rema rules (325:1); see Biur Halachah (457:1).
In addition, the fact that the cakes will be given out to different people is called lechalek, and according to many authorities there is no tziruf for challah.
Therefore, based on the two considerations, there is no need to take challah.
For the second argument, see Chalas Lechem, introduction to no. 5; Minchas Yitzchak 8:109; Shevet Ha-Levi 2:179 (at length).