The basic rule is that the witnesses to a will cannot be beneficiaries.
Also, AFAIK, spouses or civil partners of witnesses are not entitled to benefit either.
The principal act is the Succession Act 1965.
LINK
http://www.irishstatutebook.ie/eli/1965/act/27/enacted/en/print.html
Part VII deals with wills.
S.78 deals with signing and witnessing will
S. 82 deals with witness exclusion from benefit.
I am not aware of any exclusion of a beneficiary because their father was one of the two or more witnesses to the will.
HOWEVER, great care needs to be taken about "civilians" executing a will without using the services of a solicitor.
Think of how it might look if the will was ever contested.
Disgruntled objectors who considered themselves as putative beneficiaries can try and argue, inter alia, coercion and undue influence and such like.
Hovering beneficiaries might be regarded as being bad form or worse in the event of a dispute.
I do not question the probity of any of the parties for one moment but simply point out a lurking potential problem with DIY wills.
AFAIK beneficiaries have no legal entitlement to know what is in a will.
Equally, the testator has no obligation to tell any beneficiary what is in a will unless he wishes to do so.
BTW the testator can change a will at any time with no obligation to tell the witnesses or the potential beneficiaries.
In a matter such as this the only way to execute a will with legally "clean hands" - to borrow the euphemism - is for it to be dealt with by a solicitor thus leaving everyone confidently at ease that everything is objectively above reproach.