Since your son is considered to be single, you can sponsor him with a relatively short (an immigration processing goes) wait. You should do that immediately after dealing with your granddaughter's situation.
As for your granddaughter, she can get a student visa to attend a private secondary school and then the university. You There is no time limit on the holding of a student visa. You should begin immediately contacting private schools in your area to see if they issue I-20s for foreign students. You will need to pay tuition and purchase health insurance. It is unlikely that your health insurance will permit you to add her to your policy. Look at this website for schools in your area:
http://studyinthestates.dhs.gov/school-search
The issue is she needs to demonstrate that she does not have immigration intent as is the case for a student visa. I suggest that you enlist the services of an immigration attorney with a relationship with legal specialists where your son lives. Check the AILA (immigration attorneys' professional organization) to find someone anywhere in the US with services near your son's home. Since immigration law is federal practice, it is not necessary for the attorney to be near you; it is far more important for the attorney/firm to have specialized knowledge about US policies for Ukrainian citizens. You should also discuss the current situation in the Ukraine to determine if there are any options for refugee status for your son and other grandchildren.

