Well, I can understand why you would worry. There are some strange "half-signs" there, but I think you have to try to take a deep breath. If he was tested and it came back negative, that obviously is a very good indicator. Aren't those tests supposed to be over 95% accurate now? (They didn't used to be so good). With only one freckle "just above the groin area" I doubt that qualifies as the "axillary freckling" that counts as 1 of 2 "required" signs to diagnose NF. To have NO CAL's at all would be highly unusual in a person with NF. (Oh, and as for your daughter - did you know that about 10% of ALL people have 1 or 2 CAL's. So, that alone is no reason at all to worry about her. -- I have NF and I have a daughter with 2 CAL's who we are quite sure does not have NF -- they did a "family linkage study" which is like 99.9% accurate on her- it can only be done in families with multiple generations of affected people like I have).
Now as for the "freckles" - there IS such a thing as "iris freckles" and they are NOT the same thing as Lisch nodules. A well trained opthalmologist (ie: one who has lots of experience looking at lots of eyes with Lisch nodules, freckles and no "spots" at all) should be able to tell the difference I would think - but that may be hard to come by. So my point here, is that they could well be freckles and not Lisch nodules but I am not sure if you can find someone who can tell you "100%" for sure.
I really don't have much advice, just the knowledge I have about NF that says it is still "very unlikely" your son has it (and even less likely your daughter has it!). I don't know if you will ever find someone who can say 100% for sure unfortunately.
Hang in there. Glad to hear your son's health seems to be very good following his Chemo!