As for your conveyor routing logic, I'm not sure how best to help you because as far as I can tell, your items are being routed correctly. Give me more specifics regarding your routing questions, and I'll see what I can do to help out. For the most part, you should be doing your routing with the aid of the Decision Points on the conveyor. Don't use the Photo Eyes unless you want specific photo eye type behavior. The attached model demonstrates simple routing using decision points.
As for the items not placing themselves on top of the table... I think you're fighting with the internal behavior of the Processor object you used to model the table. The default position of an item entering a Processor object is down below the top of the object. You can use an entry trigger as suggested in an earlier answer to modify the z location of the item, but your next problem will be to control your robots so that their motion looks more realistic. In the attached model, I created motion paths for both the transport robot and the welding robot so you can see how this is done. I found the "Manipulation Tools" on the following Robot tab to be useful in defining the path positions.

conveyor-robot-example.fsm