i want to say those ambient effects at the beginning and end are very heavily manipulated piano (i wish i could find this video i saw where someone uses looping, reverb, and other effects on a keyboard and gets pretty much the same sounds). this song also has electronically manipulated sounds in addition to organic instrumentation for overall body-melting effect. both strive to be ethereal & blissful as possible. also, i think musical saw has a similar aural character to the aforementioned ambient effects.

It sounds like a sine-based synth arpeggio with vibrato and slow attack, drowned in reverb and delay. Maybe a filtered vibraphone synth or something similar.

In live performances they use a sampler so I'm assuming there's some tricky processing going on that can't be easily replicated live. It's possible they got that sound by oscillating a narrow EQ band up and down over a chord to isolate the component notes. But it's also possible they just sampled it out of simplicity.

Beautiful sound though. Sounds like a sunrise. Maybe I'll try recreating it this weekend. Someone else go ahead and post another song I can't do it at the moment.

Theremin is similar to musical saw, similar vocals, and it's also made by a duo.