Hi Mike
If you stay out of the big cities you might be able to find appropriate camping spots.
I have walked from Porto to Santiago twice (solo and with my nephew) and stayed away from most of the big cities. From memory I didn't see any camping spots although (I agree with Falcon) if you check with the tourist authority they may have a list of areas in which you can camp out.
Some of the albergues are out of town so that may be a solution to your needs if you can't find camping spots. They are well set up with kitchens, laundries, etc. and cater for large groups depending on how large your group is(?) The albergue in Rates is one of the first on this camino and well set up to cater for groups as is the one in Rubiaes and Valencia.
Any idea how long you and your group plan to walk daily?
The CSJ organisation has a good guide book (donativo) on the portugues route that can be found on their website
http://www.csj.org.uk that can asssist with planning stages. Also John
Brierly has some good information on his website. He has a guide book as well as a book of maps.
Good luck with your planning.
Feel free PM me if you would like any further information.