In Embedded Engineer, you can use only one initial node per activity. Multiple initial nodes are not supported.
In accordance to the UML specification, every element with no incoming control flow will be executed first if the incoming object flows have been satisfied. This process continues until the code generator encounters an element with incoming or outgoing control flow, or if there are incoming object flows which cannot be satisfied at this point.
If you have an initial node in your activity diagram, the code generator will proceed to generate code for all the elements which are reachable over the initial node. Keep in mind that it's not allowed to have a control flow from an initial node to an activity final node.