My husband (with early AD) was desperate to have an iPad because a friend of his had one so I bought him one for last Christmas. Sad to say that it has been £700 worth of a mistake, because he has never been able to use it, and it seriously upset him when he couldn't get the hang of it at all - I got it going but basically he hasn't been anywhere near it since. Now I'm the only one who uses it when we are away from the house as it's lighter and more transportable than the laptop (which he can't use either). For brain-training exercises, our psycho-neuro recommended 'Brain Trainer, 90Day Workout' book, available from Amazon, plus crossword books.
Sorry to say, but if they've lost the ability to use the laptop that they were on every day, they really can't learn the new skills necessary to use a different operating system like an iPad.
Apologies if this sounds hard, but it's how it is.