Most likely to be the relay holder thats burnt out.

The wiring and and fuse holder/relay holder is not really up to the job of coping with the current that the fans draw when they are on.

Best thing to do imo is to make yourself a new fan wiring loom with some thicker wire and with each fan having its own relay and fuse as opposed to both of the fans having one relay and one fuse between them.

Should be working perfect after that!!