Hi I am the youngest of 7 siblings. We have same mother, different fathers. the question is when my father met my mother she had previously had 4 kids, so when my dad came along my eldest sister was born the same year 1963. So my dad and mum had us 3 girls. There has always been a question is my father my sister's dad too, as some one told her in her teens that some one else was her dad. So can we as siblings be tested to see if we are full sisters as my parents divorced many years ago and 1 passed in 2000, and my dad passed in 2011. How do we go about this?

Why does it really matter ? Honestly, being a sister has little to do with sperm and who the bio father is.

DNA testing of 2 sisters will show 'something' but won't be totally accurate. For that you need to include testing of a male on both mother's and father's side (their brothers or known sons, preferably). Plan on spending about $150 each, although you may be able to find a group discount. There are many sites online.