Minimum common grounds for all sotapanna and all arahant
For stream-enterer we have:

AN6.34:4.4: But those who have experiential confidence in the Buddha, the teaching, and the Saṅgha, and have the ethics loved by the noble ones, do know that they are stream-enterers.”

For arahant we have release from ten fetters:

AN10.13:1.1: “Mendicants, there are ten fetters. What ten? The five lower fetters and the five higher fetters.
AN10.13:1.4: What are the five lower fetters? Identity view, doubt, misapprehension of precepts and observances, sensual desire, and ill will. These are the five lower fetters.
AN10.13:2.1: What are the five higher fetters? Desire for rebirth in the realm of luminous form, desire for rebirth in the formless realm, conceit, restlessness, and ignorance.

The interpretation may differ, but the above definitions are common ground.
A key point of potential dispute is the validation of &quot;experiential confidence.&quot; Historical, this was even an issue in the Buddha's time:

AN3.21:2.3: The personal witness, the one attained to view, and the one freed by faith. These are the three people found in the world. Of these three people, who do you believe to be the finest?”

For those who experienced confidence in the Triple Gem via first jhana, they would be a personal witness.

AN3.21:5.7: Because this person’s faculty of immersion is outstanding.”

For those who experienced confidence in the Triple Gem via deep study of the Dhamma, they would be attained to view.

AN3.21:7.7: Because this person’s faculty of wisdom is outstanding.”

For those who experienced confidence in the Triple Gem via faith, they would be attained by faith.

AN3.21:3.7: Because this person’s faculty of faith is outstanding.”

Yet the Buddha answered quite simply and inclusively:

AN3.21:12.1: In this matter, it’s not easy to definitively declare that one of these three people is finest.”