You need special tubes and an ultracentrifuge for it. (S. Att. pdf). Than the upper band is mtDNA, lowest band nDNA. But you can also try to dilute your DNA 1:10 before PCR, so you dilute also the impurities.

EtBr-CsCl is a time consuming and difficult procedure. There are several other methods for DNA purification using different kits or chromatographic methods where you adsorb DNA on a matrix and then elute in the desired buffer.

Partly agree with both previous answers. First thing you should focus on, is modifying your DNA isolation protocol with phenol chloroform isoamyl method and get good quality DNA. Most important thing to consider here is grind the tissue as much as possible in liquid nitrogen and dont let is absorb moisture from atmosphere. It should always be dry powder.

Add the phenol moisture and vortex as much as possible (atleast 3 min, vigorously).

Try to avoid any contamination from the interface while pipetting out the supernatant after centrifugation.

This should remove all inhibitors, if not, dilute the DNA as mentioned above.

Use suitable/sturdy polymerase, which might be suitable for your samples.

Mind that not a single polymerase work for all kind of samples.