UK citizenship app referee question re: non-relative

[vfordlcsw]

Hi,
I'm a US citizen born before 1982 to a British mum and just started the process of applying for British citizenship so I could have dual citizenship. I still have first cousins from my mum's side who are British nationals but don't have anyone else I can use for a reference/referee. I see amoungst the list of requirements that the referee not be a relative. Could I use my cousin's husband, since we are only related by marriage not by blood? This was unclear to me, but would definitely make my life easier. Also if you have any other tips for making sure I select a successful referee that would be helpful. If I cannot use my cousin's husband I will have to think of an acquaintance who may have met me at a wedding or something, this will be more challenging. Thank you for your help!