I want to use ParallelLayout to show my data which will have more split and merge (Pairs) but I don’t want to use group within graph.
First you need to identify the pairs of Split and Merge nodes and all of the regular nodes and connecting links between them, just as if they were members of a Group. You will need to make sure that these virtual subgraphs nest properly, and that there are no left-over Split nodes or Merge nodes. You need to decide what to do with any extra regular nodes that are not between paired Split and Merge nodes.
Then the layout needs to be modified to operate recursively on each of these subgraphs. A layout will need to treat each subgraph as if it were a simple node, calling the layout on the subgraph and then moving the subgraph by calling Diagram.moveParts in order to maintain the link routes within the subgraph, just as if calling Group.move.
If I get a chance later this week to work on this, perhaps I can get started on it, but I cannot make any promises at this time.