It has been a harmonious existence since the late Bob Tisch agreed to purchase 50 percent of the Giants from the Mara Family in 1991. The partnership became admired throughout the NFL as the Tisch side handled the fiscal part of the business while the Mara side focused primarily on the football decisions.

When Bob Tisch and Wellington Mara died 20 days apart in 2005, their sons, Steve and John, assumed co-ownership. They have celebrated winning Super Bowls together, built a new stadium in the Meadowlands and watched as revenues skyrocketed.

But the Tisch and Mara families could find themselves at odds over whether to fire head coach Pat Shurmur and general manager Dave Gettleman. Two sources familiar with the Giants’ thinking told The Post Tisch has seen enough and wants a fresh start with a new GM and head coach, while John Mara wants to wait until the outcome of Sunday’s season finale against the Eagles at MetLife Stadium before making a decision.

The Giants’ ownership and front office personnel likely will meet on Monday to decide the fate of Shurmur and Gettleman, who would match last year’s 5-11 record by beating the Eagles. A win would be the Giants third straight to end the season, helping Shurmur’s case to stay.

“It will be interesting to see if Steve gets his way,” a source told The Post. “He wants a change. He feels for the fans.”

It was Tisch who broke the organization’s code of silence when he spoke to sports broadcaster Bruce Beck during a charity event earlier this month. The Giants were in the midst of a record nine-game losing streak and there had been no public comment from Mara or Gettleman. The only voice was Shurmur, who expressed continued hope and confidence as his team lost game after game.

Tisch finally spoke up.

“It’s been a very frustrating season,” he told Beck. “At the end of the season, John Mara and I are going to get together and discuss the future. As partners we have to be very honest with each other about where we see this team going into the 2020 season.”

Mara has been known to be reluctant to change. Former coach Tom Coughlin had back-to-back 6-10 seasons before he was let go following the 2015 season. Jerry Reese remained as GM and hired Ben McAdoo as the head coach. After a playoff appearance in 2016, McAdoo and Reese were shown the door near the end of 2017, when the Giants finished 3-13.

Tisch is said to believe retaining either Shurmur or Gettleman is delaying the inevitable. A source also indicated that many of the contracts for luxury suites worth $12,000 to $30,000 per Giants game at MetLife Stadium expire at the end of the season and there are concerns a continued bad product on the field could impact future sales.

Tisch, a movie producer, has used the analogy that if he kept putting out bad movies, the public would eventually stop watching his movies. The same business principle applies for bad football.

There was an eerie feel to the Giants’ last full practice on Friday as players and coaches dealt with the approaching finality of the season and an uncertain week ahead. Cardboard boxes filled the locker room, gifts were exchanged and players spoke mostly in whispers.

Meanwhile, a group of assistant coaches and support staff tried to keep things business as usual, knowing they might need to uproot their families and look for new employment soon. These decisions impact more than just Shurmur and Gettleman.

“I’ve been coaching for a long time. There’s always a chance of stuff happening,” linebackers coach Mike Dawson said. “For me, it’s you can control what you can control. You’re going to work as hard as you can day in and day out no matter what the situation is. That’s the stamp you want to leave as a professional and as a coach.”

If Tisch gets his way, chances are the Giants will be looking for a new head coach and general manager on Monday — unless Mara wants to change his mind.