You can say: "Van a abrir a las 8" o "Abrirán a las 8" and as Tom said you can use the present indicative form for an action in the near future: "Abren a las 8". Also, if the opening time is always 8:00, you can use the present indicative to talk about a habit: "(Siempre) Abren a las 8"

"Van a estar abiertos" o "Van a abrir"

Van a abrir.

The present indicative form is also valid for expressing an action that will take place in the near future. For example, "Abren a las seis." or "Abren mañana", etc. You could also use the future indicative ("Abrirán..."). One last note is that if you're talking about a store, you would use the third-person singular (instead of plural).

“Van a abrir” es el correcto, como un plan.