+1 previous views above.
A will of the type queried is open to attack under the Succession Act 1965 Section 117.
S.117 imposes on the person making the will a moral duty to make proper provision for the child [children] in accordance with his means........
Link to S.117
http://www.irishstatutebook.ie/eli/1965/act/27/section/117/enacted/en/html#sec117
It does not follow that there has to be an equal inheritance left to all.
Circumstances of all must be considered.
3 of the children may be well off financially but number 4 may be relatively poor. A straight equal split might be unfair.
It can happen that there may be a serious and valid reason
not to leave a child an inheritance. e.g. the child is a raving cocaine addict who will sniff his entire inheritance up his nose. In that case it might be possible to leave that child an inheritance through a device like a trust whereby someone effectively controls and protects the beneficiaries inheritance (for the benefit of that beneficiary).
Leaving a house to one child can rankle bitterly. One idea to quell that would be to leave the house to the preferred one but impose on that bequest a liability to pay a specified sum to each of the other children. I have seen it done and there was no ill will in consequence. That said, circumstances of all the children need to be taken in to account before drafting the exact terms.
Generally, changing life circumstances can cause unintended consequences if wills are not updated periodically or in the light of specific events.
Finally, if a testator really dislikes the daughter/son in law I have seen wills whereby the bequest is only valid if the intended beneficiary is actually alive at the time of the testator's death

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