The ones saying "No" are wrong...
To party hunt, you only need ONE viable tag for the WMU in question, but all party members must be licenced to hunt that species (eg. Deer).
If the OP is licenced to hunt deer, and has two parties, each with at least one viable tag for each WMU, he/they can hunt as a party, provided the animals taken are in the WMU for which the tags are specified.
For example, if they only possess one tag for each of the two WMU's, the OP could hunt in party with both groups, but only one deer could be harvested in each WMU and then only by a member of their cooperative party (or group)... if the OP, as the land owner, was hunting in party with both groups, he could shoot both deer, but only one in each WMU. Once the number of tags are filled for each WMU, that party is done hunting... UNLESS, the second party agrees to hunt cooperatively with the new members to fill their tags in their respective WMU... they could not cross the border into the WMU where the tags had been filled.