The outer roof is supported by three longitudinal logs. It might be possible to hang the floor joist partially from them, but I have no clue if the logs can handle it. The house is located in snow zone 2.5, so there will be some pressure in the winter.
If by fanerbalk you mean Kertobalk, then a counterpart is 51x400 for Kerto-S. The question has multiple answers. Generally, Kertobalks are taller than glulam beams as they do not come in such large widths. The modulus of elasticity is comparable to that of glulam. With Kertobalks, it's fine to attach secondary beams to the side.