Is there a dispute over the authenticity or identity of the witness? It’s not actually fatal to the will because after all, witnesses can die and move away from the area completely and that would not invalidate a will, provided it is valid in all the other respects.
What is the problem with it?
There are more problems with home-made wills than home-made wills without problems. They are perfectly valid provided they are done properly. The ones which you get from the stationers are perfectly valid and nothing wrong with them provided once again, they are completed properly, not ambiguous, and properly executed.
It must revoke all previous wills and appoint executors and the witnesses must not be beneficiaries or spouses of beneficiaries.
The person who was writing the will (now deceased it seems) needs to sign their name and signature needs to be witnessed by two people who are present at the time of signing. If that’s not the case, the will is invalid.
Just because someone may not be physically capable of signing will does not make it invalid. They do however have to be mentally capable of knowing what they’re doing.
However, if they are not physically capable of signing the will someone else can sign it on behalf of the person writing the will but there must be a different attestation clause where it stated by the person signing on behalf of the person writing the will, that they understood the contents before it was signed.