What is meant by the equivalence of the two sheep in the aqiqah (sacrificial offering for a newborn)? Is it in weight, type, or age? And is it permissible to combine a ram and a goat, or a kid (young goat) and a ewe, that are equivalent in age and weight?

For a boy, two sheep, and for a girl, one sheep. Al-mukafa'ah (equivalence) means proximity in age and resemblance between the two sheep, and slaughtering them together. It is recommended that the two sheep be close in age, size, resemblance, and fatness, but this is a recommendation, not an obligation. The aqiqah (definition) is valid with both male and female (sheep), whether from sheep (Bovidae) or goats. The male is better because the Prophet, peace and blessings be upon him, offered two rams as aqiqah for Al-Hasan (definition) and Al-Husayn. It is recommended to choose fat, large, and good-looking animals.