Long-time immich user, similar problem. The issue (for now) is that only they owner of the media has write access. With partner sharing, asks you can do is read the media (and add them to albums).

What I do for now: I add my partner’s trash media (photos of receipts and other stuff one snaps pics of for practical reasons and then forgets) to an album: “please delete”. I periodically ask them to go through it and remove anything they want to keep, them have them delete everything in that album in batch.

Why this may not be practical for you, OP: you have two “trash producers”, so you’d have to keep a “trash” album for each of them (and sort trash media correctly).

What immich will do in the future : they have more granular permissions controls in their roadmap. The feature is likely to come with a greater overhaul of partner sharing. Partner sharing, as of now, is partly “broken” due to design decisions: you can’t

• write to your partner’s files
• share facial recognition data: each one needs to classify people in their pictures individually (e.g. both need to tag “Uncle Fred” individually in their own accounts)
• share memories: only pictures owned by you will show up in memories, not your partner’s

Before anybody asks: no, there’s no ETA…