Channel Island court order -change in circumstance

My husband is from the Channel Islands (Bailliwick of Guernsey). He and his partner split as she was having an affair. he set up voluntary payments of maintanance for his 2 sons and gave her the house they lived in (his family home for over 150 years).
We met and had our daughter. When she was 5months old, we were summoned to the Alderney Court as the ex wanted more maintenance. We were ordered to pay £300 per month for his 2 sons. At the time, we weren''t married, didn''t have a mortgage, husband was working, I was on maternity leave. The ex was living with her partner rent-free and had sold the house that was given to her, and she was unemployed.
A year later my husband was made redundant. I went back to work full time. We married. The ex married. I continued the payments as a goodwill gesture.
Now, my stepson lives with us, my husband remains unemployed after 4 years and not entitled to benefits due to my wages. We now have a mortgage. The ex and her husband both work and the youngest son remains with them.
Due to the many changes in circumstances, I would like to stop the maintenance. It seems, according to CSA website, that in UK I could do that, and that as soon as husband was made redundant, I should have done that.
However, due to Alderney court order, I am not sure what to do. The ex is furious that I''m even considering stopping, even though husband''s oldest boy now lives with us.

I''m sorry this is so long-winded, and thank you in advance for any advice. If any more information is needed, please ask and I will provide it if I can

Thank you