Extend WiFi range of 450TC2 router using G604T/2640T

I have Beetel 450TC2 ADSL Modem Router connected to ISPs RJ 11 (Phone Line - DSL) at ground floor of my home. All devices 3 laptops and 3 Android Phones (Yureka, Mi3 and Samsung S5) are connected over WiFi and enjoy good signal n speeds on ground floor and front half of first floor.

I need WIFI n Internet connectivity at full first and second floor and possibly 3rd floor (if not asking too much)

I have spare D-Link DSL-G604T and D-Link DSL-2640T, WiFi ADSL modem routers.

Primary DSL Modem Router Beetel 450TC2 has PPPoE Airtel Connection with dynamic ip from ISP. My DSL is on 24x7.
IP Address: 192.168.1.1 255.255.255.0

Laptops n Smartphones get anything like 192.168.1.2 - 9 at max and even more when guests are here.

I do not have option to connect the 450TC2 and G604T /2640T using wire (Phone or CAT 5/6 or Electric) as per design of house building.

I cannot use G604T /2640T as primary router.

I do see WDS setting in Beetel 450TC2 but not in G604T /2640T.

I have not changed anything on 450TC2, however i have RESET G604T /2640T and then changed following using wired lan connection between PC n G604T / 2640T

IP of G604T /2640T to 192.168.1.254
Wireless SSID n Channel to be same as 450TC2 i.e. SabharwalHome and 1
DHCP at G604T /2640T has been disabled.

No ATM/PPP settings have been configured as the G604T /2640T devices have been HARD RESET using the button provided.

Please help!