shared stem for different rhythms in voice-two notation

[Klaus Föhl]

Hello,

tiny example:

\relative c' << f2. \\ << c2. { c2 g4 } >> >>

question: the c2 is noted without a stem, it does however touch the stem of the
c2. note. Is this mirror-image ok notationwise? I am asking because an older
music sheet shows a situation similar to c2. and c2 as separate notes.

slightly expanded example: 

\relative c' << f2. \\ << c2. { c2( g4) } >> >>

The f2. should be Soprano, and the c2. Alto I and the {} Alto II, hence the
stems should be all down for the Alto, who splits only here. And because there
is one syllable to c2~g4, the indicating slur should connect these two notes.

And - is there a way to make the two notes in question engraved separately?

Cheers
Klaus