So, I've been asked to escort an elderly relative from Athens back to Australia next week as their travelling companion had to go back earlier than expected. We fly next week and I bought my ticket last night as there were only 1 or possibly 2 seats left. I have a few questions that I hope the regulars can help with and fill in my knowledge or pre warn me were possible. My relative is travelling in business class and I'm going down the back. They have requested wheelchair assistance.

1. I've bought a Y Flex fare, Booking class H apparently. This give me access to priority check in from what I understand. Does this mean I can check in at the business class desks with my relative?
2. Is there any point, nay is it even possible to link our tickets? I don't know of any benefit to do so, but perhaps the experts on here do.
3. Will I be able to stay with them while they are being pushed on the wheelchair? Do they get priority going through security and can I join them through that?
4. Will they be taken the Swissport lounge to wait? I've messaged Swissport and it seems the Athens lounge is "private" for airline passengers only. I have a Priority Pass card and it used to be accepted there, but no longer it seems. What are my chances of accompanying them in? Alternatively do they get taken somewhere else to wait?
5. At boarding, can I go on board with them to help them settle in and store bags etc?
6. On board, is it worth letting the crew know that I'm sitting in the next cabin if needed (highly unlikely as there are no ongoing medical issues, just "old age"!).
7. I've been able to preselect a seat for free, so I've opted for an aisle seat in the middle section (hopefully a couple will take the other 2 seats and not need to go over me to get out!). No Economy Space seats were available for purchase. Does this mean they have all been sold? Or do they hold some back for sale at check in etc?
8. Would I be able to check up on them after the meal services and before landing on each leg? I am not after a free meal or drink, just to check that they are comfortable etc and prepared for disembarkation (eg landing card completed for Australia). There's no chance for sneaky self upgrade as there were no business class legs for sale so I assume the flight is full (baring no shows of course!). I also wouldn't come up during the meal service or when the cabin is dark.
9. I've never travelled with anyone using wheelchairs, but I assume they will need to wait until everyone is off the plane before they are fetched.
10. We only have a scheduled transit of 1h 10 mins. Would they bother taking him to the lounge or just to the next gate?
11. If by some twist of fate we end up have a longer stay (delayed departure aircraft) would they let me into the lounge? They sell access don't they? I don't mind paying, but only if it was 2 to 3 hours or more. There doesn't seem to be any Priority Pass lounges there, just some discounts off the food from some outlets.
12. Again, I don't think I'll have time, but I hear there are some free showers - however the reviewer said they weren't of a good enough cleanliness standard to use so he didn't. Any experiences here?
13. https://www.youtube.com/watch?v=g63PwMzQ_fY
    (vlogger if you want to get down with the kids..) was very disappointed and hungry with the meals served on his flights. Looking at the video, the actual meal container looks tiny in his hands, not the larger meals promised by the advertising a while ago at launch. The "scrolls" promised as well haven't turned up in any of the reviews I've seen, just standard white rolls. And there are several who have mentioned that dessert wasn't served with the tea and coffee. Is this a requestable item then?
14. The review showed that the headphones had a unique magnetic clip. Does this mean I can't plug my Bose headset in?
15. One review showed the seat pillows doubled as neck pillows, but the linked review above doesn't mention that, so are standard pillows the norm now?
16. What's people's view of the B787 Y seat? I keep hearing it's hard, narrow and the head rest flap is pointless. Should I pack my own neck pillow and some extra seat cushioning? I do have a minor back issue currently.
17. At the Australia end, I'm assuming it's the airport authority that runs the wheelchair service, but how far do they take passengers? Through immigration (the e-gates are way faster than the manual ones, but I don't know how my relative would cope with all the instructions)? Through to the exit?
18. On the subject of security, does Abu Dhabi re-screen transit passengers as they get off the plane like at Dubai and Hong Kong, or at the gate like Singapore?
19. Are there plenty of water fountains near the gates at Abu Dhabi to refill my containers?
20. Probably a moot point as the plane appears full, but is there any point in bidding for an empty seat next to me for the 14 hour leg? Or bidding for an upgrade to business? If so, have people done so in the past and what sort of bid has been successful?
21. Is there anything I've missed than you can suggest I do or look out before we fly?

Thanks for your patience and replies in advance.