A redundancy can only happen if there is a reduction in workload to mean insufficient work for that person. If that is the case then the other events are irrelevant, as long as they have followed the letter of the law in terms of redundancy. It doesn't matter how long he's worked there or how good a worker he has been. A genuine redundancy doesn't take account of things like that as the work wouldn't be there for someone whether they'd been there a day, a month, a year or a decade and were a good, bad or indifferent worker.

Your friend needs to speak to an Employment Law solicitor and give all the facts for them to assess whether he has a claim against the charity. He definitely does not have a claim against the accountant as it is not the accountant that has made him redundant. However if the charity have not followed employment law then he could have a case for unfair dismissal and it's possible that the charity could then sue the accountant. (I have a client who sued her previous bookkeeper successfully for not advising when she should have become VAT registered)