There is no cost for google classrooms, you just need a gmail address to set one up and as long as the learner is sent a valid link from the tutor who has set up the classroom, they can join. Only those with the link code can see the work, when my learners have completed a module ready for assessment I then 'invite' the verifier to the class as an additional tutor, for them to look at the work done by the learner. Once this is done, they can them be removed again if the learner is uncomfortable about anyone else being in the same classroom. I have individual classrooms for each of my learners so that they can be confident about posting work. 

Teams also has a whiteboard function where both learner and tutor can 'draw' or write, this can be helpful when explaining concepts. Teams sessions can also be recorded - with permissions of course.