I am head of household and the only adult making income. Can I claim my fiance's children as dependents, if they live in our home majority time, & I support them fully?

The children live in my home that I share with my fiance, their father. I am head of household and my fiance provides no income, he receives child support from his ex. Can I claim his children as dependents because they live in my home majority time and I support them financially?