does residential nil rate band apply

[Campione73]

My mother died in 2019 leaving her share of her house to me in trust with the proviso her partner could remain in the house until his death. My Mum and her partner were never married. My Mum's partner has now passed and we are going through probate. We are unsure if we are able to apply for residential nil rate band for my mothers share of the house as it passed to me. I believe we are unable to apply for residential nil rate band for her partners half of the house as it hasn't passed directly to a direct relative as he wasn't my legal stepfather. Any advise please??