Yes—this is likely a mix of imperfect alignment and subject movement, which often causes halos/ghosting at high-contrast edges like people against a bright sky. Handheld HDR with moving subjects is difficult to merge cleanly automatically.

Best salvage approach:

1. Manually align the source images in GIMP as layers, using one frame as the reference. Adjust translation, rotation, and possibly scale.
2. Prioritize alignment at the important high-contrast edges (for example, where the sky meets the subjects).
3. Run the HDR/exposure blend on the manually aligned files instead of relying on automatic alignment.
4. If the people still look blurred or ghosted, composite them in manually: use the HDR/tonemapped result for the background, then mask in the best-exposed single frame for the people.

Some HDR tools also offer selective deghosting, letting you choose one exposure for problem areas, which can help with moving subjects.

In short: you may not get a perfect automatic HDR merge, but you can often rescue the shot by manual alignment plus masking/compositing the subjects from a single exposure.