Lancaster, 34, has had a tough job not only being the new woman in Stewart's life, but also earning the acceptance of his kids before the couple tie the knot.
She explains, "Of course it wasn't a bed of roses from the outset. Any young person who has to deal with a new woman coming into their life is going to take a while to figure them out."
However, Lancaster's calm approach has earned her a firm place in her soon-to-be stepchildren's hearts.
She adds, "I was just myself, I didn't try to assume any sort of role and we struck up a really good relationship.
"They have been just wonderful to me especially now. They came out to join me and Rod on the last leg of his tour and they were all touching my belly and picking out names. They can't wait for us to get married."