You use the masculine plural form when a masculine object is assumed but not specified?
I'm not sure what your context is. Here the object is definitely masculine.
Usually shnei/shtei. When people talk fast it can be just shne/shte, without the 'y' sound at the end.
Naftali I believe Emily is asking in the general. I am curious as well. When do you use שני vs שתי?
When the object is not explicit you would use the masculine form.
For general counting, however, you would use the feminine.