Hi Arjuna, welcome to Pharaoh Heaven.
Thank you for using English.
The unemployed (and the employed) do not come from particular houses. Instead, the whole city shares the "pool" of workers. Any building with access to labor will obtain employees, if there are enough workers in the city. (If there is unemployment then there are more than enough workers for all buildings that have access to labor.)
Each building that needs employees sends out a Citizen (or labor-seeker). The citizen will walk for at least 26 road tiles and then return to his building. If the citizen walks within 2 tiles of an occupied house (preferably at least 2 house tiles) then the building will have access to labor. The building will send out the citizen repeatedly, and if he doesn't pass near houses regularly then the building may lose access to labor. The Problems overlay ('T' hot key) is very useful--it shows (among other things) buildings without access to labor and their citizens.
Buildings that need employees should be placed so that their citizens walk by houses. One method is to design the roads so that regardless of the decisions that the citizen makes (when leaving his building and at intersections) he will always walk by houses. Another method is to look for buildings that do not have access to labor, and to place extra (crummy) houses near roads where their citizens walk.
Assuming that the laborers from your work camp will go to floodplain farms, the work camp should be reasonably close to those farms. If a housing block isn't too far away, the work camp could be built close to (or even inside of) it, so that it gets labor access from houses in the block. Otherwise, you could put a few crummy houses near the work camp.
Note that a citizen does not have a specific destination (except when returning to his building) and therefore will not go through a roadblock. A roadblock might be placed to prevent the citizen from a work camp from going into the floodplain. (A laborer generated by the work camp does have a specific destination and will go through a roadblock.)