ERFAs don't have nearly the freedom to negotiate with other teams as do restricted free agents (RFAs) and the grail of the open market, unrestricted free agents (UFAs), so Hoffman, Wheat and Thomas don't have a lot of options, if any, should the Cowboys opt to keep them around.
An ERFA can not, under any circumstances, negotiate with another organization.
Seeing as Hoffman, Wheat and Thomas have all accrued less than two seasons in the NFL — accrual being determined by how many games they've spent on the active roster of a team — their rights are owned, yes, exclusively by the Cowboys.
That's if the front office provides a one-year tender/offer equal to the league minimum for that position. In other words, if they want all three of these players, just pay them the minimum and it's mission accomplished for the Cowboys.