If the onus is on the new team member to ask for help when they need it, they'll have to figure out what difficulty and quantity of questions are considered appropriate. That's pretty stressful to try to figure out remotely. Much easier for them to have a senior person looking them in the face and asking "How'd it go yesterday? What questions can I answer for you this morning?"
When in office, there is a lot of unstructured conversations. I have found that having 2 hour blocks of video conf 'coworking' do help a lot there in terms of surfacing questions in an unprompted and organic way.
Have you tried holding "office hours" for the newer guys? i.e. give them a window when they can ask their questions to the other devs?
Have you given them an idea of what you expect from them when they're stuck? example here: https://medium.com/@JeffLombardJr/for-new-devs-how-to-ask-in...
People will be on different schedules, but it is nice to have a weekly sync at the beginning of the week. Gitlab and Zapier have alot of great resources on setting up remote teams
- https://zapier.com/blog/survival-guide-to-remote-work/
- https://about.gitlab.com/company/culture/all-remote/guide/