I suspect the problem you're having relates to your "2 stream data set"? If you have arrays, this is simple - bundle the arrays and connect to an XY Graph.
Perhaps you mean you're getting a subset of points each iteration of a loop, and you want to append these to a graph?
In that case, you can use one of 3(?) formats - an array of points (cluster of X and Y), a cluster of arrays (X array, Y array) or an array of Complex numbers (Re, Im).
The 3rd option is quite straightforward if you use the Build Array and Re/Im to Complex nodes.
A comparison of the methods can be seen here:
Comparison of bundling options
This was taken from another thread I answered, but hopefully it's clear that I have two individual DBL numbers (one for X, taken from the difference in time, and the other for Y from the string conversion over serial port) and I'm creating 3 different arrays on the Shift Registers (you only need to pick one of these options) and connecting it to an XY Graph (named Buffer).
You can get a link to the other thread if you're interested to read more by clicking on the image, and under the kudos/download buttons, there should be "publishing history" or similar. This thread and one other will be linked.