is it possible to configure a 3825 router with 2 source interface and 2 destination for NetFlow?
for sure you cannot use two different sources and about double export destination:
yes, you can in 12.4
NetFlow Multiple Export Destinations: Benefits
The NetFlow Multiple Export Destinations feature enables configuration of multiple destinations for the NetFlow data. With this feature enabled, two identical streams of NetFlow data are sent to the destination host. Currently, the maximum number of export destinations allowed is two.
The NetFlow Multiple Export Destinations feature improves the chances of receiving complete NetFlow data because it provides redundant streams of data. Because the same export data is sent to more than one NetFlow collector, fewer packets are lost.
If you needed you could try to NAT the source of export packets on another router in the path to the second destination.
Hope to help