Old Model Decals Peeling and Lifting - Need Help

    Misting on some  warm water? some decal setting solution?, some Future?

Misting verses Spraying  so the very small droplets would give some control of how much your putting on and may soften them just enough to use a paint brush to gently push them into place

I would try decal solvent if the setting solution does not work.  Solvent is more agressive and makes the decal softer and stickier.

With a notable exception (eg. Gunze Mr Mark Setter, which contains an adhesive) or two, generally speaking, decal solvents/setters won't help much if the decals have lifted due to lack of adhesive.

Some decals just aren't that sticky when they are made and sometimes, bad application practices, eg. over-soaking can cause loss of adhesive from the decals.  

If you can get it, brush on Future.