Praise be to Allah.
The aim behind the ‘aqeeqah is to shed blood for the newborn, because every newborn is held in pledge for his ‘aqeeqah.
There is no report in the Sunnah about dividing the meat of the ‘aqeeqah, because the primary aim of the Lawgiver is the sacrifice; this is why a great deal of attention was paid to it and it was strongly encouraged. This is the apparent meaning of the words of the Prophet (blessings and peace of Allah be upon him), “Every child is in pledge for his ‘aqeeqah which should be sacrificed for him on the seventh day.” Narrated by Abu Dawood, 2838; classed as saheeh by Shaykh al-Albaani in Saheeh Abi Dawood.
Ibn Abi Shaybah (8/53) narrated from Ibn Sireen that he used to say: “Do with the meat of the ‘aqeeqah whatever you want.”
Ibn Qudaamah (may Allah have mercy on him) said:
Ahmad was asked about it and he quoted the words of Ibn Sireen. This indicates that he followed that view. He was asked whether one could eat it all and he said: I did not say he should eat it all and not give anything of it in charity. End quote.
If he wishes he may eat it all, or if he wishes he may share it all out among the poor and needy, or if he wishes he may eat some and distribute some. End quote.
If the father of the child slaughters the ‘aqeeqah then gives it all to his sister for her wedding, there is nothing wrong with that, so long as he himself does the slaughtering first, or it is done by someone appointed by him to do it on his behalf with the intention of doing the ‘aqeeqah. If he slaughters it with this intention, then he has done what is Sunnah, and after that he can do whatever he wants with the meat; he can give it all, or some of it, to his sister for her wedding, although it is preferable for him to eat some of it and give some away and give some in charity.
But if he gives the two sheep to his sister for her to slaughter them on the day of her wedding, then he will not be fulfilling the Sunnah of ‘aqeeqah thereby.
And Allah knows best.