The rules you're citing are the general rules for harmonizing, which are generally applied for classical 4 voices harmonization - and usually for the same family of instruments.
When dealing with an ensamble, those rules still apply, but that mostly depends on two aspects:
- the instruments (type and amount) that are going to play a specific voice, and the octave they're playing it;
- the harmonic/musical result you want to achieve;
For instance, consider a simple string ensemble: you could have 8 first violins and just one doublebass, this doesn't mean that those violins can't play the same note.
Doubling voices (even for the same type of instrument) changes the "colour" of the harmony. It's not just about the dynamic each voice reaches, but the harmonics generated by that amount, also counting the harmonics each instrument has.
So, unless we're talking about a melodic movement (melody or counterpoint), doubling rules still apply according to the result you want to achieve. If you need a more balanced result (close to what you'd do with the same harmony using 4 voices), then you should also consider balancing the doubling in the same way, considering how those instruments's sound results and is perceived and possibly the amount of players for that section/voice.
BUT. That also depends on the style you want to use. For instance, in classical/early romantic style, it was common to have some instruments to double notes that are generally not doubled; a classic example is the usage of timpani and trumpets, which often doubled leading notes or thirds just because those were the only notes they could play, but since they added a more "triumphant" result, the doubling wasn't a problem.
Then again, doubling notes that are normally not doubled is not that an issue, especially if their voice has some importance (consider the E/D# bass/cello "pedale" in the finale of Beethoven's 7th), and in more modern styles those rules (like almost any other rule) are obviously much less strict, so the choice depends on the musical result you require.
 Historically, timpani and trumpets only played the tonic and dominant of the whole composition tonality; this was due to technical and practical reasons: natural trumpets were common even in early 19th century, mostly because the more advanced valve trumpets were more expensive and difficult to build, and it was also rare to find virtuoso players, so composers didn't "push" their limits on those instruments by using basic root/fifth notes and specifying in which key the instrument was (coincidentally, the habit was kept for long time exactly because of this: since the repertoire didn't require high skilled players or advanced instruments, players rarely became skilled). The same for timpani, but mostly due to technical issues: modern foot-activated timpani was created only in mid-1800, before that they could only be tuned by turning each screw of the head, so it was almost impossible to change tuning while playing (even between movements).