I have done exactly what you are asking. DW and I went to Europe in 2017 with another couple for 4 weeks, touring. We all had cell phones to connect to the local wifi, along with laptops and/or tablets. We had at least 8 devices, or more to connect. I took a small travel router. We connected all of our devices to the travel router, and whenever the travel router connected, all of our devices were automatically connected.
However, I always had to manually connect the travel router to the local wifi. There is no way to "automatically" do that the first time. The problem is that there are usually multiple wifi sources, and you are only authorized the one provided by your host. Also, there may be a security password that must be entered.
So, no, there is no way to "automatically" log in a wifi, but, yes, you can manually log in a wifi, once, at each location and your other devices would then "automatically" be logged in.
Now, as far as your home wifi and your personal hotspot, once you have logged the travel router into them one time, it will auto connect to them from then on.
This is the one I have and am well pleased with it. (This one can connect via wifi or via ethernet cable.)
