Lot of important questions.
“How does one that is liberated through wisdom come to understand the rebirth process if they don’t develop the divine eye or other abhinna power to observe it?”
One gains wisdom not by seeing previous births, but by seeing the anicca nature. One can see the anicca nature of this life itself.
– However, not believing in the rebirth process is a micca ditthi, and thus makes it impossible to see the anicca anture; see, “Micca Ditthi, Gandhabba, and Sotapanna Stage“.
“Is there some sort of indirect evidence that becomes apparent as one practices Satipatthana?”
Satipattahana is the way to be mindful and to discard bad vaci sankhara; see, “Correct Meaning of Vacī Sankhāra“.
– Please also read the Satipatthana sutta in the “Sutta Interpretations” section.
“..but never believed in rebirth simply due to the increasing animal and human population in the world.”
This is also very important to clarify. Living beings include not only humans and animals, but beings in all 31 realms; see, “31 Realms Associated with the Earth“.
– There are basically an infinite number beings in all 31 realms. Fluctuations in human and animal populations are compensated by births/deaths in other realms.
Please ask questions on anything that is not clear. These are VERY important issues to resolve.
Also see: “Buddhist Explanations of Conception, Abortion, and Contraception“.