I am decorating and have a problem with painted walls.

Paint is striping off like wallpaper in some areas .

Problem 1. Must I strip all this paint off or can I just paint over it ?

Problem 2. Where the paint is solid I now have a hard line between the
paint and the plastered wall. Will "Base Coat" hide this line or do I have
to feather it back possibly exposing more loose paint?

Any suggestions welcome