Does every member of a family living in the same house have to sacrifice an animal each if they have nisab amount of wealth?

I live in a four-people family: my brother, me, my mother and my father. My brother works with my father; I work in a different place. My brother is engaged; I am single. We sacrifice only one animal every year in eid al-adha. Is it necessary for us to sacrifice a separate animal each? Or, is it enough to sacrifice one animal for the family?

Dear Brother / Sister,

Every member of the family who is sane and has reached the age of puberty has to sacrifice an animal if he has the necessary conditions. 

For whom is it wajib to sacrifice an animal?

The following conditions are necessary for a person for the obligation of sacrificing an animal:

1. To be a Muslim.

2. To be free.

3. To be a resident. Not to be travelling on the days of eid al-adha. 

4. To be rich enough to give sadaqah al-fitr. The nisab amount for zakah and sadaqah al-fitr is 80 grams of gold or 561 grams of silver.  

5. To be sane and to have reached the age of puberty. The fifth condition is controversial among the imams. According to some imams, it is not necessary to be sane and to have reached the age of puberty for sacrificing an animal to be wajib. It is necessary to sacrifice an animal for rich children and mentally ill people. Their guardians will sacrifice animals for them.

Questions on Islam