wrote:

(snip)

Should I just forget about this whole thing, or make an issue about it? I
know they might be better off with this woman, but they might not be either. A
admittedly I'm guessing at that simply because I know there are two other cats
and two people in a small trailer. But at the same time, I keep having this
thought some little kid is still missing his orange cat.

If there is a residential area nearby, post signs asking if anyone is
missing an orange tabby female w/kitten. If there is an original owner,
(doubtful, imo), (s)he can probably make a strident enough demand on the
sister of the woman who allegedly has the cats to get the information
needed and secure their return.

I would be more concerned about the relocation of an outdoor adult.
Unless the person now in possession of the cats keeps the female
confined, there is a good chance she will try to go back to her
territory, probably with kitten in tow. This usually means traveling
some distance across inhospitable and dangerous terrain. Cats become
disoriented and reckless; most don't survive the trip.

If I were you, I would revisit the woman whose sister supposedly took
the cats. Tell her whatever you need to in order to see the cats. Tell
her you want to get the female spayed (This needs to be done before she
becomes pregnant again.), that you want to treat the cats for fleas,
contribute food, you're despondent over the loss of the cats, whatever.
It is very odd that the woman doesn't want you to speak with the new
"owner". It's cause to be nervous.