... then you can pick parts which use a somewhat smaller ensemble. Below are some suggestions on such parts.
Soprano solo with woodwinds, marimba and strings
Mixed choir with cor anglais, tuba, percussion and strings
Double choir solo a cappella (alternatively double quartet)
Four soloists (Soprano, Mezzo soprano, Tenor, Bass) with woodwinds, trumpet, percussion and strings. Solo role for the viola.
Tenor solo along with horn solo, plus woodwinds and strings
Three soloists (Soprano, Tenor, Bass), mixed choir and chamber orchestra
Four soloists (Soprano, Mezzo soprano, Tenor, Bass) assisted by ladies choir, along with woodwinds, percussion and strings
It is also possible to consider other alternatives if it helps you create a performance. There are piano reductions available for some parts and more can be made (or perhaps versions for organ).
Another suggestion is to pick the parts which concern those Human Rights which have your particular interest. Just check the text out, simple as that.
At any rate make contact and let us know if you have ideas.
The most common words in the Human Rights Declaration are "Everyone" and "Freedom". Initially each of those words received an interval - a starting point from which their melodies could develop. Check out the below two PDF files.
The below PDF "Annotations" lists the different parts and the related Articles. Additionally it provides info on the musical background and building blocks like keys / modi, melodies, tempo, inter-relationships between different parts, and more.
Here is a PDF with comments on the Oratorio and each of its 19 individual parts.
It is 7 pages and discusses text interpretation, the composition process and
other musical matters. Plus issues on performance.