Hi Marco,
not sure what your problem with filleting is ?
Do all large fillets first then the small ones.
Attached your test with fillets.
Cheers
Barry

Ps: just found a problem with your large fillet where you have tapered it from front to back you have 3 edges created by the fillets converging at the front so when trying to add a fillet on the front edge no go.
I selected the 3 edges of the top ran 0.7 fillet and second fillet points for a 0.4 fillet at the back and that is what I have posted.
Are you trying to get the side fillets to match the front fillet where they meet at the front ?