It’s complicated. Ultron sure was using the twins to fulfil his plans of dropping Sokovia and wiping out the human race. We know he was planning this all along from Vision’s dream when Wanda reads his mind.
Wanda Maximoff: How could you?
Ultron: How could I what?
Wanda Maximoff: You said we would destroy the Avengers, make a better world.
Ultron: It will be better.
Wanda Maximoff: When everyone is dead.
Ultron: That is not...! The human race will have every opportunity to improve.
Pietro Maximoff: And if they don't?
Ultron: Ask Noah.
Avengers: Age of Ultron
However, Ultron comes from the Mind Stone, Tony and Banner: he is an extremely clever AI. He has emotions and can display them as we see throughout the film. We see this quite clearly in the scene when Vision talks to the last Ultron and when Wanda rips the heart out of one of them.
It’s also worth noting that Vision is part Ultron. As we know Vision and Wanda have a very close relationship, romantic even. Whilst their journey together brought them closer I think the part of him that was Ultron might have played a part in it too.
Ultron certainly seems to care for the twins, especially Wanda. However, he also wanted his plan to come to fruition no matter what: he’s kind of like Thanos in that aspect. He wants to save the Earth (universe) no matter the personal cost to himself.
I think it’s worth noting though that we don’t know if Ultron would have saved Wanda and Pietro had they still been on his side at that point. He could have saved them by just keeping them in the air during the “meteor”.