How can an expected grandchild also obtain an EB-5 green card?

If your daughter is unmarried under age 21, she is included in your I-526 petition. Her expected child cannot be included in your I-526 petition. Once your daughter obtains her lawful permanent resident status when she immigrates to the United States with you or adjusts status if in the United States, she can file for her child. Please contact your immigration attorney or another experienced immigration attorney to discuss the specifics of your case.

You can add the new child after I-526 approval (when actually applying for the visa at the U.S. consulate).

After the child is born you would include the child in the I-485 application along with the parents. Bring the birth certificate to the interview for a visa at the U.S. consulate in your country.

No, the grandchild will not be included. You can try for humanitarian parole for the grandchild and if not granted, have the parent file for the child once he or she is a permanent resident.