Hey!
Congratulations on the interview invite!
I haven't had a panel interview with quite that many partners, but from my own experience with panel interviews, I'd keep in mind that it is still ultimately a conversation rather than five separate interviews. I'd try to engage with whoever is asking the question, while also maintaining eye contact with the rest of the panel where it feels natural.
In terms of preparation, I'd make sure that you are particularly comfortable discussing your motivations, experiences on previous schemes/work experience, commercial awareness, and why this firm specifically. As this is a DTC process, they are often assessing whether they can see you as a future trainee and colleague, and you need to make sure your enthusiasm comes across in a way that you'd usually be able to on a vacation scheme.
For questions at the end, I wouldn't put too much pressure on yourself to come up with something incredibly unique or technical, and just ensure that it isn't something that you could find online yourself. I've found that the best questions are often the ones that you are genuinely interested in hearing the answer to. If you know who will be interviewing you, you can definitely tailor some questions to particular partners and their practice areas. Equally, you can ask questions to the panel as a whole. In the panel interviews I've completed, they often just take it in turns answering, which can give you some really interesting insights into different perspectives across the firm.
I would also prepare a few more questions than you think you will need, as there is always a chance one or two get answered naturally during the interview.
Wishing you the best of luck - reaching the final DTC interview is an amazing achievement, and I'm sure you'll do great!
