I've had some more clarification about who you can apply for and how it works:
An airline may choose to have a totally own-branded selection process and therefore their own application website, but neither easy nor JMC have gone for this. One of the early questions an applicant will be asked by CTC McAlpine is which schemes they would like to apply for. At the moment those available are JMC, easy and CTC McAlpine's own. The application will then be processed on the basis of the answer to that question.
The first 4 stages of selection are common to all 3 schemes. If CTC McAlpine believe a successful applicant is particularly suited to one of the sponsoring airlines and they have indicated that they are keen to apply to that airline, then they will refer the applicant to that airline. This does not mean that those not referred to an airline at the start are lower quality applicants – each airline has its own culture and are after subtly different kinds of people.
Although both easy and JMC have chosen to adopt cadets at the selection stage, it's probable that other airlines may decide to commit to an individual part-way through training. This may be partly because the airline may wish to have more information about an individual's progress, and partly because an airline's manpower requirements may only be finalised weeks before they need those people in service. An airline must select cadets before advanced training commences, as the type ratings are not generic and are flown with that airline’s SOPs (and, obviously, on the appropriate type).
In terms of numbers, JMC and easy may, if they wish, pick up more than the 4 and 24 rcadets espectively from the first 12 months’ 72 by committing to extra cadets during training. CTC McAlpine anticipate having airline places for all 72 by the end of intermediate training; in fact they’re deliberately aiming low to avoid a hold pool at that stage until the market's demand becomes more clear.
If someone has applied to an airline and not been selected, they can apply again for another airline (or direct to CTC McAlpine). However, there are no plans at the moment to allow second applications after any given period. Therefore, if someone has failed one of the first 4 stages of selection, there will not be a second opportunity via an application to another airline in the scheme. In other words, apply for the lot unless you really don’t want to work for a particular airline!