Hello Victoria,
Always nice to make someone glad!
I can't get further back in time. There is a town/part in Germany called Spandau, nearby Berlin:
https://www.google.nl/maps/place/Spandau,+Berlijn,+Duitsland...Maybe they originally came from there? But I can't prove it.
How nice that you were in Groningen , the place of your great grandmother's family
There were also Spandeau's sailing for the VOC (Verenigde Oost indische Compagny, sailing on Indie), but the only one I can find who seems to be connected to your line is
Roeloff Bernardus Spandauw,
registred as ''missed'' in 1785, from Heerenveen (Friesland)
Good luck and regards,
Jettie