Using 2 or more estate agents will work out to be more costly. We sold a house 5 years ago using two estate agents, one local and one nationwide. They both worked together and shared the advertising costs, website costs etc but there were individual costs pertaining to each EA.
One the house went sale agreed, both EA's were paid half the overall agreed fee each.
It's was easy to negotiate with both of them at the start of the process, not sure how OP would fare out if the house is currently up for sale with one agent already.