Combine data from two sources with same format

Is it possible to combine data from two sources with same format (BEAST) using dump1090-fa?

Yes, as long as only one source contains contains timing information or if MLAT is disabled.
MLAT cannot handle non-GPS timing information from multiple sources.

It is often easier to combine the information using VRS or PlanePlotter.
VRS virtualradarserver.co.uk/
PlanePlotter coaa.co.uk/planeplotter.htm

Thanks for the answer!