There is no word for siblings in french, you would have to say i have so many brothers and so many sisters.
J'ai (the # of sisters) soeur et (# of brothers) frère.
'Fratelli' is an Italian equivalent of 'siblings'. It's a masculine noun whose definite article is 'i' ['the'] and whose indefinite article is 'dei' ['some']. It's pronounced 'frah-TEHL-lee'.