Short answer: Isomers have little to do with understanding the diversity of life.
Isomers are compounds that have the same chemical formula but different structural formulas.
One of the reasons for biodiversity is genetic variations.
Genes are subunits of DNA. Each gene contains a particular set of instructions. It usually codes for a particular protein.
There are only four different chemical bases in a gene (adenine, thymine, cytosine, and guanine). The order of the bases determines the function of the gene.
Each gene consists of thousands, even hundreds of thousands, of chemical bases.
If two of these genes had exactly the same number of each type of base, then they would be isomers of each other.
But that is extremely unlikely. If a gene has just one different base or one more base, it is no longer an isomer. It is a different compound.
Isomerism has little to do with the diversity of life.