Clare Haslam, 44, and Deborah Clifton, 49, from Chorlton, were hit by a Ford Focus outside Withington Hospital in south Manchester on Tuesday.
A man, 89, was arrested on suspicion of causing two deaths by dangerous driving and has been bailed, police said.
The couple, who had a child, "were made for each other", their families said.
"Clare was popular and well-liked by many, she was so full of life, but as a young lady she was really lacking in self-confidence until she met Debbie.
"Her and Debbie became inseparable and did practically everything together including raising their adorable little girl.
The families said Debbie was "so excited about the news of a new grandchild on the way" and her "large, loving family will miss her very much".
Clare was a "much-loved daughter, sister and auntie" and "we are all so heartbroken", they said.
"Clare and Debbie were like an old married couple, they would fight like cat and dog, bicker at the slightest thing but ultimately they were made for each other, so blissfully happy and without doubt soulmates."
Greater Manchester Police said an investigation is under way and thanked the public for their help.
The families of two women who were run over and killed in a hospital car park have paid tribute to the "blissfully happy soulmates".