Nigel.  I'm afraid that if your other two trees are already visibly affected then it's more than likely too late.
You can not only treat the trees yourself if they are saveable but also apply preventative treatment.
An aside to Rita, I think it's Sospalm who will be doing the presentation.
When I first realised that the infestation was moving up the coast towards us last year, I contacted Sospalm and purchased the necessary components.  The guy offered to deliver them to me when he was passing and whilst here, closely examined the big shade tree next to the house and said he didn't think it was infected but that I should apply the treatment anyway.  I had a rough winter healthwise and didn't get around to treating the tree until a few months ago.  It was too late and it's now dead.  I have a group of four about 100m from the house which I'm now treating in the hope that I've caught them in time.  We drove from Santa Barbara to Tortosa yesterday and were horrified to notice how many trees have succumbed in the last few months.  It's a crying shame but too late now to save them.
For more information, Google "Red Palm Weevil" and in particular Sospalm.  Preventative (and in some cases curative) treatment can be applied at not too high a cost.  The only possible difficulty is applying foliar spray if your tree/s is/are very tall.  The other part of the treatment involves injecting the trunk and or mixing the chemical with irrigation water.  Sospalm will sell you the components and Sol D'Ebre sell the chemical (Confidor) that is used for both methods of application.  If anyone has any further questions or would like advice, please fire away.