Good afternoon Michael.
you would need two connectors per floor of each tower. the connector sprues are these:
link
On each sprue you find the two connectors for each floor ; ground, middle, exposed/parapet floor, they are in this order on the sprue in the picture.
As you wish to have the wall sections meeting at 90 degrees on each tower, when you build each layer of the tower you would have to set the two connectors for each floor side by side.
the sprue of connectors you want to use in this case is the one on the left from the picture above, from the Warlord web site, as the other ones are to be used for walls connections at a different angles.
I hope this helps. If you are still not sure, I would suggest to build the wall sections first, then start by building the first layer of the tower without gluing the tower walls – possibly using blue-tack – and see that you are using the right components for what you have in mind.
This video could also provide you with further insight:
link
Lorenzo
Warlord Games Customer Service team