Once you have set up a Dynamic Group for each house in Data Digger, you can then send members of each House a text via the Comms package on ScholarPack (if you subscribe to this).
Head to Reporting > Data Digger
From the dropdown at 1 select School House, then another dropdown will appear for you to select the House name. A number will appear in the centre of the blue circle, which will be the number of students in that particular house. Click on the number and save this group by that House name.
Repeat this process to produce a Dynamic Group for each House (which means as students enter and leave that house the group will be updated).
Now, if you go to Admin > Comms, you will find these House groups under Dynamic Groups in order to select all members to receive a Comms message.