Try to extract all the objects from libone.a and libtwo.a then merge them all together:
$ ar -x libone.a
$ ar -x libtwo.a
$ ar -r -c libcombined.a *.o
this should recreate the index. Anyway, from the man page of ar:
The ordering of members in an archive can make a difference in how programs are linked using the library, if a symbol is defined in more than one member.
this may bring to complications.