Why not start with the original Dark Souls? It's the perfect time to play it since it just got a Remastered version.
Between Dark Souls 3 and Bloodborne I would say that Bloodborne is the more accessible game while Dark Souls 3 is the easier game for beginners. But you should know that if you want to enjoy Dark Souls 3 as much as possible then you need to play the original Dark Souls first.
Well I thought about it but if I am correct Dark Souls 1 is considered the most difficult one from all souls-games including Nioh and Bloodborne and to be honest I wanna get familiar with the gameplay first before going for such a difficult game^^