I think the easiest way for you to do what you are talking about is going to be to have 3 apps in your project: your top level app, a “professional” app and a “client” app. At the top level app, all you really need to do is give the users a login form, and 2 links, one for registering as a Professional and one for registering as a Client.
In this case, I believe it will be easiest for you to use Django’s built in Permissions system, and assign each type of user to a corresponding group (eg. professionals and clients). You can use a decorator on your views to ensure that only members of a particular group can access that view (since you have 2 separate apps for each group, you can add a decorator to all views in each of them, or you can import Django’s authorization functions into your urls.py and check it there, although that is beyond the scope of this answer).
Registration is easy enough, use your urls.py file to forward the user that wants to register to the correct app. Once you do that, you should be able to use django-allauth registration on each app, allowing you to create 2 different kinds of users. Make sure when the register, you assign them to the correct group membership.
As for the login redirection, once you receive the POST data, I would check for which type of user logged in, and use that to forward the user to the correct URL that goes with the Professional or Client app. You can see the below link for an idea of redirecting a user after login.