ABDESSALEM wrote

1- A way to ensure the link between LAN1 and LAN2.
2- If possible to distribute the load between the first link (AP1 with AP2) and second link (with AP3 AP4).
3- if the first link down the second link provides the connection

1-what do you want to ensure, you do not provide info. you call the four APs that can't be, two have to be Clients
2-what do you mean by load, if the only thing you want is two Laps to see each other, as your sketch, box 2 7510s
3-thats normal, you have to separate AP1-AP4 minimum 4 mts. the others too.
Question for you
Distance of the link

See This image

http://www.mediafire.com/view/wi32o97lhf39x33/How_to_configure_the_bridge.png

AP1 Connected with AP2 mode Bridge

AP3 Connected with AP4 mode Bridge

Distance of the link is : 1.1 Km

Thanks.

ABDESSALEM wrote

AP1 Connected with AP2 mode Bridge
AP3 Connected with AP4 mode Bridge

Bridge mode sucks, it's a reapeating mode, use AP mode on one side and Client mode on the other
I don't see the reason to use 2 extra devices on a link that works with 2

No, your topology in the picture creates a loop ring, which will cause broadcast storm and finally break down the network.

I haven't seen any wireless load link backup yet. But if you have load balance routers you can achieve the same goal in a more complex way.

Another solution is to buy two CPE510, they are much better products and they are 5G 300Mbps access points.

ABDESSALEM wrote

See This image

http://www.mediafire.com/view/wi32o97lhf39x33/How_to_configure_the_bridge.png

AP1 Connected with AP2 mode Bridge

AP3 Connected with AP4 mode Bridge

Distance of the link is : 1.1 Km

Thanks.