Are you sure you want a merge? Usually merges don't have the same variables in each dataset, or if they do, you need to rename the variables so they're unique in the final data set. You can't have multiple variables with the same name.
I think you may want to concatenate/append the data instead. You'll have the same issue though, variables with the same name MUST have the same type in a single data set.
http://support.sas.com/documentation/cdl/en/basess/68381/HTML/default/viewer.htm#p19t3r1gxavpoin14jdd23gcheve.htm
I show a method to identify which variables in are in which datasets here, but you can modify it to also show type.
https://gist.github.com/statgeek/3b57ae085d9f7a36a2d95c15f04e72e6
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