Another approach you could use that is pretty close in appearance, is to set it as a single table with row and column spanning. I mocked this up in DITA XML (shown in Oxygen) but it is a standard table model so it should render in XPP pretty much the same.

You could play with table rules to give the illusion of a table within a table. Here's my XML tagging:

Thanks Jay and John for your input

Let us know what you end up doing, Shahnawaz

Sure

Finally I splitted the table into three parts and achieve the output. 

Whatever works! There's almost always more than one way.

Whatever works! There's almost always more than one way.