DNA testing question

[FenellaBestwick]

There has been a lot of lying & abuse in my family. I suspect that my mum & her sister are only half sisters. My cousin suspects the same. We are both NC with our dm's. If my cousin & myself did a dna test, would it, through us the offspring, prove our mothers situation?

I don't know enough about how the percentages of matching DNA correlate to degrees of kinship, but, I would expect that if you and your cousin are not as closely related as you suspect, the % of matching DNA would fall outside the 'normal range' for first cousins.