House deposit gift from boyfriends dad

I’m buying a house in England and received my mortgage offer from Barclays a few weeks ago. Im buying the house just in my name but my boyfriend will be living there & signing an occupier consent form.

(Boyfriend isn’t on the mortgage due to his poor credit score and a black mark on his credit report)

My boyfriend’s parents are gifting me around 40% of the deposit. Mortgage broker aware of this & solicitor aware of this. I’m going through the gifted deposit process with solicitors currently. They’re happy to sign standard gift letters - confirming it’s not a loan, they don’t expect repayment or a stake in the house.

Stupidly, I’ve been googling & am now worried because my boyfriend’s parents aren’t my direct relatives.

I’ve seen mixed reports on if they class as direct relatives or not and whether they’re allowed to gift the money.

For context, we’ve been together 7 years and have lived together whilst renting for the last 6 years.

Mortgage broker aware of source of gifts but unsure if they advised exactly of source of gift.

Given there’s no chain, we’re hoping to exchange next month & solicitor thinks this is possible. But given gift source, how likely is it that mortgage lender will see this & revoke offer ahead of exchange?