Hi, hope I can help.
Learning vocabulary and knowing vocabulary are two different things. Seems as though your group are good at the learning side and that is a good start.
I would encourage them to use the macmillan dictionary (available on-line free or cheap download app). This dictionary has a system of red words and red stars. These indicate the most frequent 7,500 words and they are the important ones to learn and know. Focus on the red words, and lots of work in putting them into sentences, making lots of meaning using them.
Students can write them on little cards and shuffle through them a few times a day, until they really know them.
I'd also be tempted to make up some games with their words - a simple board game, when students land on the word they must put it into a sentence.