I must be just lucky, but ...
All these problems! I've got an iPhone. I've passed one on to someone else. Various family members have changed from iPhone to Android and to Windows. Others, friends and colleagues have moved in both directions. None of us seem to get this problem, in two different couintries. I even notice that, when iPhone correspondents go out of wifi range, messages suddenly seem to have gone over SMS, including when abroad.
As for using Whatsapp as an alternative - just post your details on Facebook or Twitter to cut out the middle man. Oh, you use Google tools. Carry on.