The way I learned and internalized English, was through programming and a vocabulary trainer/flash cards at around 11 years old. So my advice would be: find something they find interesting and provide them with mostly English resources to learn that interesting thing, while also starting to learn basic vocabulary through flash cards.

I went through the effort to guide some people (mostly my family n≈10) through distrochooser, but in the end most of them chose Linux Mint and two wanted to go with endeavour for gaming, but I installed base arch on it and we designed their basic workflows together. For now everyone is happy.