Language / półtora/półtorej - do they decline? [5]

Yes, your sentence is correct.
"półtora" is used for the masculine gender and "półtorej" for the feminine gender.
In your example you have "mieszkańców" - this is the masculine gender thus "półtora" is the correct form.

Law / UN or NGO's organizations in Poland [7]

Hello Lonman,

try with un.org.pl and then go to Instytucje ONZ w Polsce (UN = ONZ Organizacja Narodów Zjednoczonych in Polish). Unfortunatelly all of them are located in Warsaw.