Who has legal right to claim dependents during seperation prior to divorce?

My daughter & her 3 children lived at my home last year/2009. She & her husband were seperated. Their divorce was not final till Jan. 2010. I provided a home, paid utilities, phone bills, bought her a car, paid for school supplies, school clothes, school pictures, yearbooks, field trips, etc. for the children. Her husband did not give her any type of child support during last year. I had planned to claim her & the children as dependents on my 2009 tax return. But now the ex-husband is saying he is claiming the children.
(They did not live with him but did go for weekend visits). How can I remedy this situation? I am afraid if I claim them & he does also, there will be an IRS audit & a delay in receiving my refund. What can I legally do to insure that I am able to claim the children as dependents? My daughter only worked part time last year & made only $1300.00 last year which she received a 1099 form. She did receive food stamps & medical benifits for the children, but all other support for her & the children was from me. She & her husband were also seperated in 2008 & filed Married filing seperately & he did not use use the children as dependents. Now in 2010 that he has been court ordered to pay child support he feels he should claim the children as dependents. (Even though my daughter has not received child support as of yet.)