I had the exact same problem last week. We had a monster huge settee bed that had seen better days, and wanted to get it down two flights of stairs in a very tight area. It took almost a morning getting it up there in the first place, and so we weren't thrilled with the prospect of getting it down.
The lovely British Heart Foundation on Old Kent Road kindly offered to send a couple of guys round to take it off our hands (and also down the stairs...)
When DFS delivered the new settee, the blokes just laughed at the idea of taking the old one down. My fear was that the BHF would send round a couple of elderly charity workers, who would struggle, and we'd be taking the piss.
I put in a polite call to BHF, who were very understanding.
Anyway - the solution - a simple saw and half an hour later the settee was in pieces. Lambeth Council then took it away, as agreed. I was amazed how simple it was to cut it up - 'top quality' settee as well
Unless the old settees really are worth saving, I'd go for the cut 'em up approach.
BHF: 0844 499 4164