What was the name of Lavan's wife, the mother of Rachel and Leah?
I have seen Adina mentioned online, but I don't have a source...
The sefer Tiferes Shlomo al HaTorah in Parshas Vayetze brings a number of answers to the question of how Yaakov was allowed to marry two sisters. One of the answers is that Rachel and Leah were born to Lavan from two different wives and therefore not prohibited to Yaakov. In light of this, you may have to change your question to "What were the names of Rachel and Leah's mothers?
Adina. It comes from The Book of Enoch, I believe.
It's also in Jasher 28:28 Adinah This book is also mentioned in Genesis.