Will these versions work fine for wireless connection?I have 5 routers under 2.8.28.1 AP and 4 clients.i want upgrade all these routers to 2.9.12.If I update my AP to 2.9.12 first, other routers under 2.8.28 works with AP?
checked.works 
yes it works, but in 2.9.12 there is an improved wireless driver. it will work best if all your routers will run that latest version