Either “We sold them (the) clothes,” or “We sold (the) clothes to them.”
“To” or “for” are only used when the direct object comes first. The choice between “to” and “for” depends on the verb. With “sell” we use “to” to introduce a direct object. (You can use “for” as well but that has a different meaning! We sold them clothes for him. We sold clothes to them for him.
We sold him clothes to them.)
Yes the translations are increasingly garbled (but not in the wrong tense, like this one), partly because the sentences are more complex and partly, I think, because people drop out of the course. This means fewer error reports coming in.
I completed the tree twice and saw a lot of reported errors fixed in the earlier lessons. You are at least helping the course developers if you keep going to the end and report the errors. They have a massive amount to do though. No wonder progress is so slow.