Alfie, sorry to read this. I don't think there is much that can be done - some lymphoedema nurses can do a special massage that releases some of the pressure but I don't think it will help your pelvic / scrotal swelling. We did have a member some time back who ended up with a catheter because the swelling was so bad, but I suspect that would be a last resort?
It is good that you have a lymphoedema specialist nurse to support you but have you also been referred to your local hospice / Macmillan nurses / maggie's centre? Sometimes, they have ideas and facilities and access to things that your NHS nurse cannot offer - I wonder if it would be worth checking out? And have you been seen by a physiotherapist or occupational therapist? They might have different ideas.
As the doctors are now saying months rather than years, have you started to apply for benefits? These are available to everyone who could reasonably be expected to have less than 6 months but many oncos are happy to sign them for someone who is thought to be in the final 12 months - it is about 'reasonable expectation' rather than 'definite'. The hospice social worker or macmillan / maggies worker could probably help you complete the forms.
https://www.mariecurie.org.uk/help/money/benefits-entitlements/living-with-terminal-illness/special-rules