Advice needed! Refinancing parents home

[Samantha Hooten]

I need advice! My parents own a home in near San Diego, CA it right now it’s worth about 970k. They suggested we refinance a loan of 600k with me on it. My fiancé and I make about 10k a month and the new mortgage payment estimates are between 4-5k. Right now we would pay half but when my parents pass I would take over full payments and rent it out. Rental estimates on Zillow and in surrounding neighborhood are at 4k also. Right now we have our own mortgage of 1400 and a car loan of 16k.

For more context, they took out a loan with Unison (terrible idea, they know now) and it would be about 300k to buy out the unison loan. I am also military. 
Does this sound like a good investment? Or should I just let them sell the home?