Praise be to Allah.
‘Aqeeqah is a confirmed Sunnah, but there is no sin on the one who does not do it. Abu Dawood (2842) narrated from ‘Amr ibn Shu’ayb that his father narrated from his grandfather: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “Whoever has a child born to him and wants to offer a sacrifice for him, let him offer a sacrifice, two sheep of similar type for a boy and one sheep for a girl.” The hadeeth was classed as hasan by al-Albaani in Saheeh Abi Dawood.
If a person did not offer ‘aqeeqah for his children, because he was not able to, or because he did not know about ‘aqeeqah, it is mustahabb for him to do it after that, even if it is a long time after.
It says in Fataawa al-Lajnah al-Daa’imah (11/441):
A man had a number of sons and he did not do ‘aqeeqah for them, because he was poor. A few years later, Allaah made him independent of means by His Bounty. Does he have to do ‘aqeeqah?
If the situation is as described, then it is prescribed for him to do ‘aqeeqah for them, two sheep for each boy. End quote.
The father may do the ‘aqeeqah for his grandson, as the Prophet (peace and blessings of Allaah be upon him) did for his grandsons al-Hasan and al-Husayn, as was narrated by Abu Dawood (2841) and al-Nasaa’i (4219), and classed as saheeh by Shaykh al-Albaani in Saheeh Abi Dawood (2466).
Based on that, if you want to follow the Sunnah properly, then offer one sheep for the first son, to complete what his grandfather did, if the grandfather offered only one sheep, and there is nothing wrong with that. But if you leave it as one sheep, that was sacrificed by the grandfather, that is fine.
Some scholars are of the view that ‘aqeeqah comes under the same rulings as udhiyah (sacrifice) with regard to how it is to be disposed of. So it is mustahabb to divide it into three parts; one third for yourself, one third for your friends, and one third for the poor.
Some of them are of the view that the ‘aqeeqah is not like the udhiyah, so he may do with it whatever he wants. Please see question no. 8423.
Whatever the case, if you did not give anything of the ‘aqeeqah to anyone else, it is still valid. As for udhiyah, the one who eats it all and does not give any of it in charity should replace it with the smallest amount that can be called meat, such as an uqiyah etc., which he should buy and then give it in charity. See Kashshaaf al-Qinaa’ (3/23).
Based on that, the ‘aqeeqah for the second son has been done in full, as has that for the third son. Praise be to Allaah.
We ask Allaah to bless you and your children, and to make them a help for you in obeying Allaah, and a treasure for Islam and the Muslims.
And Allaah knows best.