Something not right about the numbers. 90 cows year round is probably too many for 100 acres. Depending on many factors, 30 to 50 might be a better number. With 90 cows on 100 acres, you will probably need WAY more than 5 acres of hay. Investigate the numbers more. Is it 90 cows? How many bulls does he have? How many hay bales does he feed per year? How many bales did he buy last year? How many calves does he sale each year? Where did he sell them last year? How much did he get for them? What kind of tractor and equipment does he have? Regardless of the answers, I think you will find that the best case would result in income less than the poverty level.
Are there engineering jobs in that area? There are some counties in SC with mostly timber and farming and little other employment opportunities. Don't quit your job and relocate without a business plan - which I think will require a lot more information than you have so far.
If the goal is to take care of family and keep some cattle, look at cutting way back on the cow numbers in order to have minimum input costs. If there is some year round grass, look at cow numbers that eliminate or minimize hay usage. Maybe that is only 10 or 20 cows. Find a good job first. You then have adequate income, able to take care of family, able to still look out in the pasture and see some cattle, able to keep grandpa's cattle operation going, just at a much reduced level. You won't be a cattle baron on 100 acres.