Basing on the pronounciation you are most probably looking for Pyrcz (no Pyrch surname in Polish; 'cz' is pronounced like 'ch' in 'cherry'): http://www.moikrewni.pl/mapa/kompletny/pyrcz.html
and for Stanuch (no Stanuk surname in Polish; 'ch' is pronounced like 'h' in 'history', which is somehow similar to 'k' at the end of word): http://www.moikrewni.pl/mapa/kompletny/stanuch.html
As you see none of those surnames was recorded in the Lubaczów county (where Niemstów is located) recently but they have concentrations in the south-eastern Poland.
Btw. Are you sure you are looking for Niemstów in Lubaczów county (historically Austria-Hungary/Galicia) and not for Niemstów, Lubin county (south-western Poland; historically Germany)?