Dear Felicity, so very, very sorry for your loss, it all sounds so sad.
Can you get a solicitor to tell you what your rights and obligations are? I dont think that we have enough knowledge or information to say.
A thought, but if his ‘legal’ next of kin want a funeral their way, then it might be best to let that happen and you could have a lovely memorial service with your mutual friends and colleagues, and your family.
My MiL, much loved, died in her own home on another continent. She had a brief funeral service attended by my FiL, her husband, and local friends. Several weeks later we went over with other family and friends and organised a memorial service for her in a lovely area of countryside near their home, followed by tea in a nearby restaurant. It was a very beautiful occasion.
I do very much hope that all goes as well as possible at this sad time ?