Non-expert there, but here are my two cents:

we share 99% of our genes with a chimpanzee

If you sequence your DNA and the DNA of a random chimp, and consider only the substrings that can be identified as genes, and measure string similarity between them, you will get a number between 98% and 99%, depending on the choice of string similarity measure (there are many reasonable choices).

95% of our genes with a random human

Never heard that before.

50% of our genes with a sibling

Suppose an unique id tag was attached to all the gene strings in the DNA of each of your parents. Even if the same gene appears in both of your parents, or even if it appears multiple times in the same parent, each instance gets a different id.
Then your parents mate and produce you and your sibling. On average, you and your sibling will share 50% of these gene ids.
Of course, many of these genes with different ids will be identical strings, hence the genetic similarity measured as in the human-chimp case will be > 99.9%.