This may work, but depends on the type of system you have. Elgato Support says the following: https://help.elgato.com/customer/de/portal/articles/1491132-wie-viele-displays-können-zusammen-mit-elgato-thunderbolt™-dock-be-used-.
I don't think the MacBook 2009 has a Thunderbolt port, only a mini Display Port. They look identical, but they are 2 different ports. That's why it can't work either