Have mercy on us! Lori Loughlin’s daughters, Olivia and Isabella, are begging the Full House star, 55, to take a plea deal after she and husband Mossimo Giannulli, 56, were hit with additional charges in the college admissions scandal. “They’re terrified that Lori could end up spending the rest of her life behind bars,” spills a source close to the disgraced actress, who’s facing up to 60 years in prison for allegedly paying $500,000 to get the girls into the University of Southern California. “But if she’d just pleaded guilty, like Felicity Huffman, she would’ve been out of jail by now!” The Desperate Housewives alum, 56, was released three days early from her 14-day prison sentence at the Federal Correctional Institution in Dublin, Calif. — otherwise known as “Club Fed”…