Try to implement a locking mechanisme that prevent two user from entering data for the same object at the same time.
There are some javaactions available in the community commons module to do this.
We implemented out own mechanisme that is not only used for locking separate objects but also for locking batches of object in case of transactionscoping of bulkupdates/creates.
My assumption is that when one of the user changes something of this object the object gets committed to the database. Then you can do the following. In the community commons you have the action objectHasChanged. You could use the microflow timer widget https://appstore.home.mendix.com/link/app/27/Mendix/Microflow-Timer (note that at the moment there are two entires for this widget in the appstore, make sure you get the latest) to trigger a microflow that uses this Java action to check if a refresh is needed. You can then use another community commons action refreshClassByObject to force a refresh of the object.
Note that you still can run into troubles. Both could still change the object before the refresh check has taken place. I would recommend the locking mechanisme that Rene suggested. You could then let the other user open the object in read only modus. And with the method above the read version would still refresh when the other user changes the object.