Hi Sirrichie
A4- This has to be your new Name, as you have changed your name.
B2- This is bit tricky.. after lot of search, I found that information on your Passport/BPR has be to same, you may face problem while going out of UK.
If you have decided to change your name you can apply to change your passport as well, to keep BRP/Passport with same info.
Section D: with above two info, this should be clear to you now, as you need to mention your old name here.
I would recommend you to discuss about your B2 to some solicitor, as you can see I haven’t got much information on this forum which is related to BRP card.
Thanks,
Ali