I normally get very annoyed when someone here replies with "Why don't you google it?". But that's exactly what I'm going to suggest. If you google the name of the relevant airline, together with the words 'special needs', you should find everything you want to know.
For example, googling 'ryanair special needs' brings this up straight away:
http://www.ryanair.co...ns/special-assistance
Just an additional (and unrelated) point. I sometimes get asked to help friends (who are often elderly) with booking domestic flights (or flights between the UK and Ireland). The first thing I always ask them is about what type of ID they have. Some airlines (e.g. Ryanair) will ONLY accept a passport or national ID card for their security purposes. Others (e.g. easyJet) will accept things like a bus pass. Make sure that you match up your neighbours' ID to the requirements of the airline you book with.
Chris