I think it is quite easy for us as outsiders to say, "Yes get in touch, you may regret not doing so" and I agree we've all had the "If only I'd asked earlier moment." However, we don't know the situation in this case and Devonshire obviously feels that it would upset her grandparents if she went behind their backs.
That is the whole point Groom, Devonshire’s grandparents feel she has gone behind their backs once and could possibly do so again.
The only way to resolve such an issue is to talk to them and reach a resolution.
Devonshire has already stated that they brought her up after the loss of her parents that being so they know what properties they have instilled in her, whether that is to blindly follow instructions or to tread her own path whilst being aware of other’s feelings.
Hopefully the bond is strong between them that ensures mutual respect and understanding rather than blind obedience.
Personally I think that there does come a time when we have to remove our Genealogy hats and just accept that people feel so strongly about something that we have to let it go, as much as we'd like to find out the truth. It isn't worth digging up things, opening old wounds and perhaps starting new family rifts. Others may feel differently.
I totally disagree, you mention finding the truth, if someone is frightened of the truth then they do not deserve respect. We may be ashamed of our past actions but it only by accepting the truth that we can move on and make amends for what we are ashamed of.
This does not mean I think Devonshire’s grandparents have done anything to be ashamed of, (before anyone reads that into my words) as obviously we do not know what has taken place.
Cheers
Guy