Also - the one which has the Signal source as ethernet keeps disconnecting

@TUMAS 

Check this TP-Link FAQ: General questions about Ethernet Backhaul feature on your Deco

@Alexandre. My setup is how its stated in the link you sent me. I have main deco connected directly to the modem then the other two decos are connected directly by cat6 to the modem. Why is one marked as ethernet and one wifi? the one with the etherner is flapping also 

@TUMAS 

What is your Deco mesh Operating Mode? You can that it in Deco app, under Advanced:

@Alexandre. It's set as wireless router(Recommended) however when i try to click on access point it wont let me.. How should it be? I have all my decos connected with independant CAT6 cables to the modem

@TUMAS 

This is from the link I provided:

In Router mode: Only the main Deco could be connected to your home modem/router. Other satellite Deco units should be connected behind the main one, just as the “Star Network” shows. If not, they may be in a network loop and cause unexpected dropout issues.

@Alexandre. So the second port of the main should connect directly to the switch?

TUMAS wrote

@Alexandre. So the second port of the main should connect directly to the switch?

@TUMAS 

Yes, this is how it works for Deco mesh running in Router mode.

@Alexandre. Ok so I connected the switch with thw other two decos to the second port of the deco and now both decos have ethernet as signal. Is that the best way to be configured? Is all the bandwidth passing through the deco like that being its own bottleneck?

@TUMAS 

This is the only way to configure Deco mesh running in Router mode, if you want to have Ethernet backhaul on Satellite Deco.

If you want, you can change Deco to Access Point mode. You'll lose very many features offered by Deco, but in AP mode you can wire Deco units any way you want, including connecting them all directly to your ISP router.

I do not need anything from Deco other than WiFi coverage, my Deco mesh runs in Access Point mode.

You said you had problems switching Deco to AP mode, I suspect it were because your WiFi mesh was unstable. Now that it is properly wired for Router mode, you can try again. After you see it switched to AP mode, you can rewire Deco units the way you want.

If in Deco app you still can't switch from Router to Access point mode, I suggest you create new post with corresponding subject, and see if someone or TP-Link support can assist you.

Does not matter how Decos are wired, assuming you use gigabit switch and knowing that Deco M5 have gigabit ports, it is unlikely your home network will experience bottleneck. Even if you keep everything as is, in Router mode.