YOU SAID:

My sister's sisters are also my sisters, and my sister is a sister to my sisters

INTO JAPANESE

私の妹の姉妹も私の姉妹であり、私の妹は私の姉妹の姉妹です

BACK INTO ENGLISH

My sister's sister is also my sister and my sister is my sister's sister

INTO JAPANESE

私の妹の妹も私の妹であり、私の妹は私の妹の妹です

BACK INTO ENGLISH

My sister's sister is also my sister, my sister is my sister's sister

INTO JAPANESE

私の妹の妹も私の妹です、私の妹は私の妹の妹です

BACK INTO ENGLISH

My sister's sister is also my sister, my sister is my sister's sister