I am asking for scientific evidence for the claims why they are extinct.
It should be shockingly obvious why they are extinct. They all died. They are extinct for the same reason that wooly mammoths are extinct, they all died. What more of an explanation do you need? We have their fossils. We can compare those fossils to modern hominids. Guess what? None of the modern hominids match the fossil hominids. What more need be said?
You believe they exist however there is no hard scientific evidence they ever existed.
No need for belief. They left fossils for us to study.
The fossil record surely doesn't support it. Scientists have said it themselves.
No, they haven't. Scientists agree that these fossils are transitional. What they debate is the exact placement of these species into the family tree of hominids.
If you disagree that these fossils are transitional then please tell us what features a real transitional would have.
If apes are still alive today then why not the half human-apes?
Because they went extinct. What more need be said? Do you likewise believe that wooly mammoths never existed because they are not alive today?
ALL living species today have evolved from ancestral species that are now extinct, a pattern repeated and repeated and repeated in the fossil record, AND a pattern that is evidenced in the cladograms developed from the DNA evidence.
We also have living species that have a mixture of characteristics from divergent taxa. Look at the platypus. It has a mixture of reptile and mammalian features (e.g. leathery eggs and fur). Platypusses are transitional even if they are not ancestral to placental mammals. So we have the very species that Cryto is looking for, and yet Cryto does not accept evolution.
As you mention, we also have ironclad DNA evidence that demonstrates shared ancestry between us and other apes. Transitional hominid fossils are just the icing on the cake.