7wk son has bili total of 8.1. His direct is 1.0. Normal stool and urine. Hida scan Monday. What are chances of biliary atresia?

Not biliary atresia . That's direct. Check for both hemolysis and causes of hepatitis; these range from very serious to trivial and self-limited.
Low. While that direct of 1.0 is a bit elevated at 7 weeks, he mainly has indirect hyperbilirubinemia. Combine that with normal urine and stools, and I'd say the chanel of biliary atresia are low.
> than zero, < 100. Is your son breastfed? If he is this level can be at the upper limits of normal for a breastfed infant. Is he otherwise eating well, gaining weight well, and have normal looking stools? Biliary atresia is possible, but there can be other factors at play. Was his direct coombs negative or positive? What is your blood type and what is his? All these factors are important to consider.