Yes, Main Deco will transmit WiFi and mobile devices can connect to it. You can see in Deco app which devices connect to what Deco.

@ArchDevil This will work just fine. Also note that Third Deco will connect wirelessly to either Main Deco or Second Deco.

@Ingo_W Yes, you can wire multiple Decos, but it must be done the proper way. This topic is discussed here: General questions about Ethernet Backhaul feature on your Deco

@ArchDevil This is possible, as long as it is done correctly. See this FAQ document for more information: General questions about Ethernet Backhaul feature on your Deco

@ZZLOW If you are getting 100Mbps from Main Deco, your Satellite #2 shouldn't get more than 25-30 if you can daisy chain it. Which means, not different from what you have. Buying more powerful Deco...

@ZZLOW If you happened to have M4 hardware V4, there should be configuration option to do that: How to select a preferred signal source on the Deco App If not, see this document: Is the Signal Source...