So they are some documentations which says how AmigaOS 3.x behave in which situations? Do we have chance to find them are there opensource?
It is nicely documented how the API has to behave in the developer documentation from C=.
Also if it is in API level completable why AROS can not do same as morphos even it needs UAE in some how?
AROS 68k is pretty compatibe. AROSx86 has the problem of the inverse endianness with the processer which makes sharing stucturres between a 68k app and a x86 OS pretty complicated, It is easier in that case to just use UAE. Note that recently there are improved approaces for AROS to get better 68k comapbility/usability.
Also note that AROS just isn't that progressed yet as MorphOS is already. But it gained pace.