@SAcouple welcome to the forum. You will get all the answers (plus lots more) here.
No, you definitely do not need a commercial organisation to organise this for you. It is incredibly easy to do it yourself.
Save yourself (a) money and (b) angst, and not be locked into a timetable, itinerary, accommodation, walking distances, that may not suit you.
Pack yourselves a couple of light backpacks with only the bare essentials for your walk. Lots of packing lists on this forum, but as you are only going for a few days many will be overkill. If you plan to stay in hotels and pensions you will not need any sleeping gear, if you want to experience the "whole thing" and stay in albergues, then you will need sleeping sheets and/or light sleeping bags. Otherwise just the clothes you will walk in that you can wash each night (so quick dry). Comfortable walking shoes. Normal ones. There are lots of cobblestones on the route out of Porto (I actually like Skechers for cobblestones, although I'd not use them for a long camino).
Get yourselves a credential each - that entitles you to stay in the pilgrim accommodation. Available through this website (go to "Services in Santiago by Ivar" on the masthead).
Find your starting point in Porto - the tourist office will point you in the right direction - and follow the yellow arrows. It is that simple!