Electrolytic rust removal is a good alternative to remove rust while preserving good metal. On the negative side rust spots will turn into pitting, this will be pronounced on the horn hilted keris
Please experiment with some scrap metal to see if you like it/you haven't done it before if you decide to go this route.
I think light etching with your preferred acid and not stained such as Jean's example is more appropriate for both blades, but this might be personal preference, some blades look better with contrasting pamor, some don't. I have good result with phosphoric acid for light keris etching and also preparing my other restoration projects prior priming it with zinc chromate/iron oxide (I'm a rust hater).
Wax is a good alternative to oil and demand less maintenance.
As the rust is old/stable, it doesn't have to be removed if owner can live with it, this is the safest alternative of all.
I'd like to hear other members opinion on the origin of the horn hilted blade. It has no pamor as far as I can tell. Is it attributed to Palembang as well?