We give our employees time to take sabbaticals. One person took 6 weeks and hiked the El Camino trail in Spain. We actually have to encourage people to take time off :)
Jokes aside, that's a really admirable - and in my experience, rare - thing you're doing. Your employees are really lucky.
Overlap it with public holidays, and you can get 17 or 18 days off in a row for 10 vacation days - 10 weekdays, three weekends and a public holiday or two. But it's usually better to plan a public holiday somewhere in the middle because of the extra traffic.
As terminology though it's not a sabbatical either. 6 weeks off sounds more like a gap between jobs with gardening leave or travel or some other project that wouldn't fit in a work vacation.