Advice needed

I live with my two autistic daughters since my wife and I split back in 2023.  I met someone new last year and all is going well so we're looking to move in together next year sometime.

I'm looking as to how to approach with the girls though.  One daughter is still retisent I think to accept the new partner and grumbles when she comes round.

My Psychologist said to me a while back that parents splitting is like a death sometimes and can take up to two years to accept however I'm wondering on the best way to approach this next step.

Gut instinct is to be direct with them and just explain that she'll be moving in however that won't affect the relationship that I have with them.  I tend to find that being honest and direct is the best way so there's no misunderstandings.

What's others' thoughts and any other methods of managing this to make the ride less bumpy for them?