I am supposed to create contents for an association that have no visual identity or anything

Hello everyone!
I am student in graphic design, and I have been a member of a horse club for a while now. When the person who was in charge of the social media and actually the communication of the association in general (nothing fancy, but we have a website, and facebook/instagram.

The administration’s council was complaining about how members would not get involved in the different activities and events, that we were getting less applications and less reactions from publications (they were barely posting anything to be honest). When I heard about it, I offered to take care of it, as I have the skills for it, being a student in graphic design, and it would be an opportunity for me to practise and have a more concretes experience of the job before I apply to any agency or other jobs.

However, the more I am trying to get things done, the more I am becoming frustated about the whole arrangement. The only graphic element they have to give me is a logo in pdf, that needs to be redesigned, they told me briefly they wanted to communicate more on social medias to show the conviviality and the cheerful atmosphere that we have at the stables, during competitions days, and all... and that we needed to post more often, and very fast after each events.

yep, thats the only thing I got. I know for a fact the club is 60 years old, that their main color is the green as in the nature, and the reference to the forest the club is situated in, and they have that fragmented horse in the logo, but they seem to never have actually thought about having a visual identity, a chart in order to have some kind of directions for the creation of the content. That leads us to some design with illustrations that do have a dynamical and convivially send information, with a website way more neutral, no dynamisms on it, and so and so on.

I have been trying to get them to think about a brief I could use to work on the visual identity and then start working on the contents creation, but they seem to have absolutely no interest doing that, and just keep asking me to post contents, or at least send them the designs for them to publish. Even more, most of the time, one of them actually do some "design" and make some presentation and just directly publish it without even talk to me about it "because we need to publish it immediately". I am feeling like they don’t acknowledge me and my ideas at all, and not even considering that I may even offer them pertinent creations. That is quite hard as I feel it has punch really bad my self esteem and my confidence in my work legitimacy...

I have been advised (kinda? not really) to just go and get set on a visual identity by myself to show them and starts the talks with that, but I dont know how and where to get started without a clear brief, with the goals and the target audience and everything clarified. what would you do?