You can’t run any significant charity entirely on volunteers, to have been able to manage with just 2 members of staff with what they’ve had to deal with from Mermaids is extraordinary. Their major people can be seen on their website here https://lgballiance.org.uk/people/
Kate Barker is listed as CEO that will be one salary (not to be confused with Kate Harris who is a trustee). The other member of staff will be her assistant. As others have mentioned staff costs are rather more than just salary and may include temporary staff. I’m pleasantly surprised they are so low.