Does a single animal sacrifice suffice, or are two sacrifices obligatory for the father's and mother's vow, similar to a vow for their son's recovery, taking into consideration their financial circumstances?

Undertaking a vow (nadhr) is disliked and does not avert Allah's decree. A conditional vow becomes binding if it is explicitly stated in a form indicating commitment, such as "It is Allah's right upon me that I slaughter an animal for my child." Both the father and the mother are obligated to slaughter a sheep if each of them vowed to slaughter for their child, and the vow of one does not suffice for the other. However, if the intention of the vow is in the heart without utterance, then nothing becomes binding. And whoever has a vow binding upon them and subsequently becomes unable to fulfill it, then the expiation for breaking an oath (kaffarat yamin) becomes incumbent upon them.