They’re made by a Swedish firm with a long pedigree in speaker production. They have always included Linkplay modules with tailored versions of firmware from the same stable as WiiM, much as other third party system integrators have done (like Edifier etc)
Yes. Yes. Yes, with each other and with your WiiM devices.
Edit: if you download their own Audio Pro app, you’ll see they share a very common look and feel with the WiiM app - indeed, you’ll see your WiiM devices there too, just not with all the features you’ll see in the full WiiM app. One thing the audio Pro app does have that I’ve asked WiiM to include for WiiM devices is a “talk to Alexa” feature which acts like a software remote mic.
Edit #2: I think we need WiiM to answer my earlier query re Alexa/ AlexaCast as the Amazon product pages now have no mention of either