Hi there,
My name is Nesim and I am more then happy to help you out with the question you have.
First of all since your using wordpress you should download JETPACK plugin which will allow you many many more things then just posting your blog posts directly to social media but also help you view your data about your visitors, speed up your website and much much more.
So my number one recommendation to do is simply by downloading and installing jetpack which indeed has the option to post your blog posts directly to your social media including instagram.
You would just need to login to every single social media account through your jetpack plugin.
Hope this answers your question,
Best Regards,
Nesim