I manage my ISA and SIPP and my wife’s ISA. On HL i can access hers from mine, although I have to log in to hers to actually trade. She doesn’t do investing. 
One for the development team. Request and accept to share someone else portfolio.
As a Dad to be this summer I was planning to set up my first Junior ISAs, so that would be also needed when FT get those up and running at some point.
That sounds like a KYC and AML nightmare if you wanted any control over it
Also I’d worry about financial control by having visibility over a partners account
Maybe it would be too much of a pain. I think HL did have send us both letters by post - so that would be the same address 
I do like this idea.
We manage our finances as a couple and having to ask my wife for her phone to view her portfolio is a good first world problem.
I frequently use the HL app to switch between our portfolios. They do have some limitations but at least you can view.
I don’t know if this has now changed but I can trade on behalf of my brother on HL.
Would love this feature for my other half on Freetrade so I can manage her SIPP and ISA for her. This feature would be great for attracting users with higher than average deposits.