Q.Spearmint
Would spearmint do well under grape vines? Is it safe for the grape vines because of their ability to take over?

No, I would not recommend Spearmint has an underplanting.
The Mint plant is highly invasive, and would best be grown in a container to keep it from invading into--everything!
Here is a link with more information.
https://www.gardeningknowhow.com/edible/herbs/mint/invasive-mint-how-to-kill-mint-plants.htm
https://www.gardeningknowhow.com/edible/herbs/mint/how-to-grow-mint-plants-in-your-garden.htm