EDTA act as cation chelating agent. hence it is used in DNA isolation to chelate the Mg++ ions which are necessary in activity of nucleases so your DNA will be safe in presence of EDTA. but higher concentration of EDTA might hamper the further reaction since it should be optimized. Tris-HCL act as stabilizing buffer during isolation of DNA, which maintain the pH of buffer.

Tris HCl is used to maintain the right pH for DNA isolation. It also interacts with the lipopolysaccharides present on the outer membrane which helps to permeabilize the membrane. EDTA is added to accelerate this effect.

After the nuclear membrane has broken, the EDTA is used to remove DNase from the environment.

I agree with Sunil Kokane