Does anyone know if I can get British passports for my grandsons 6 and 4 grandmother is British and my son is applying for his citizenship and up passport can his children then get theirs

Does anyone know the company used by matkirk in her original post? Our son is in the process of applying for his UK citizenship (British mother & American father) but our daughter-in-law would like to explore the possibility of citizenship for their two sons, both under 10 years old.