@Thehouseofmarvels - I would point out that you are relying on English law which does not apply in the OP's case. However, since, unlike those of us who actually know the law, it seems you have to rely on solicitor's websites, here are two from solicitors that specialise in this area which set out the law more fully than those you have referred to - www.willclaim.com/claim-types/contesting-a-will-time-limits/ and www.georgegreen.co.uk/site/george-green-blog/contentious-probate-disputes-how-long-do-i-have-to-bring-a-claim.
To deal with the some of the many other mistakes in your overnight posts:
In addition if brother did the probate forms properly he would have needed to write the details of who was a beneficiary
No, he would not. The forms do not ask for a list of beneficiaries.
Esentially those people would have been the new owners
Even if it were the case that they were listed on the probate forms, this would not make them the new owners. That does not happen until legal title is transferred.
If he put the names of all four beneficiaries they became the legal owners of the estate and still are
Completely wrong. See the last two points.
Why would the land registry only put his name on anything if for people were listed in the probate forms
Because beneficiaries are not listed on the probate forms and the Land Registry don't get a copy of the probate forms when transferring legal title anyway. All the Land Registry need to transfer title is an Assent from the executor and a copy of the grant of probate (which does not list the beneficiaries - it can't since the executor does not have to list the beneficiaries when applying for probate).
for the brother to get his name on the property he would have needed his siblings to sign papers rejecting their inhearitance. You can't just go to the land registry ' oi put this house in my sole name, my parents died with no will and my siblings told me verbally/ haven't mentioned wanting anything'
Complete rubbish. As per my last comment, all he would need to do is show that he had the necessary authority (grant of probate) and he could go to the Land Registry and transfer the property to anyone he wanted.
I will ignore your scenario involving a special needs sibling since that is very different from the OP's case and includes circumstances which may persuade the court to allow an out of time application even if there is no fraud.
I refute your claim there is no fraud. Either the brother claimed to be an only child on the paperwork, or he pur the names of his siblings on the paperwork and failed to tell them.
He did not put the names of his siblings on the paperwork as there is nowhere for him to put them. The form for someone dying intestate simply asks how many children they had. It does not ask for their names or give any indication that they should inherit. The siblings were all clearly aware of their mother's death. They all assumed that the estate went to the oldest son. If he knew that his siblings should inherit then yes, there may be an argument that there was fraud. However, if, as appears likely, none of them were aware that the siblings should inherit, this is not fraud. It is a mistake, and the time limits apply.
Just to say again, the above is based on the law in England and may not be correct in the OP's case which is in Northern Ireland.