The mother gave up her parental rights on paper and notarized it. Can she still take our kids off island

The mother of my children is going to take my children off island to a complete stranger. However she had given up and signed her parental rights. I am employed and have a stable and safe home for them. I support my daughters. Their mother has no place to stay or any income to support my daughters. How will I be able to get full custody for my daughters?