Yes, I’ve been doing this for some time now, using input threads (even from different processes) sending messages to one output thread, and Cloverleaf handles the acks just fine.
Are you looking just to send them back to the source or just kill them on the engine. If you are looking to return them to the source it may be a bit tricky but very doable.
How can you have two feeder systems on separate sites feeding one outbound? You’d have to have an outbound from one site feeding the other site which still gives you two inbounds feeding one outbound on the same site.