Question: When you are talking to a 3rd person, fundamentally

> 
> (1) それは、**私達**の出来あげたものです。  
> 
>  (2) それは、**われわれ**の出来あげたものです。
> 
> 
> 

mean:

> 
> That is something that we all created together.
> 
> 
> 

With regard to using them as **first person, plural, possessive pronouns**, this a nuanced choice. `I'm not asking about using them as subjects, objects, topical nouns, etc. Just as possessive pronouns.`

* My feeling is that #1 is about taking more direct credit for what was accomplished? It sounds rude? Like you considered yourself the lead in a small group of 4 or 5 people?
* Even if you were the lead, always express to outsiders that *a team of equals*, among them yourself, accomplished something? That is choice #2?

Answer: 
There are no such differences in terms of nuances that you point out.　Both are not rude and can be used for 4,5 people.
私たち and われわれ are always interchangeable without making the sentence rude or improper.

Instead, it changes an impression a bit. われわれ sounds slightly more academic or political while 私たち sounds slightly softer.
Or I can say われわれ, in any grammatical situations, is more used by male speakers. But it's not strange at all if women use われわれ.
Essentially, both mean "We". In my experience 我々 has the nuance of a "we" within a defined group: we (our class, our company, our country), where 私達 has no nuance. A very common use case is 我々日本人