Hi Peter. I think both Autoharp and Dulcimer can be used successfully, depending on your goals and the seniors' physical/mental status....(AND the two instruments sound GOOD played together).
If you are trying to create instant music, I'd suggest the Autoharp. Bedside tables can be moved to the room you're playing in and usually can be lowered to the patient's elbow height...to make it easier for them to play and see the bars. Two people can play the autoharp at the same time as well.....one for the bars, one for the strumming. Takes some co-ordination between them, but gives lots of giggles while trying. You can also use indelible ink pens to write the names of the bars larger. SOMEwhere in these threads is LOADS of two chord songs. If the patients have specific songs they enjoy singing, but you can't find the right chord for a specific note,.........just DON'T strum while singing the note. bg