nether portals not connecting correctly.

I created a Floating Islands world to play with some friends and after getting a nether portal we spent several days building to another floating island. So, we figured we would build another nether portal to move between them faster, but after building the second nether portal we went through and found ourselves at an old nether portal that had gotten blown up via a gast (sorry can't spell). Just a few blocks (20 - 40) away from our home island nether portal, but the real problem was that both (in the nether) portals went to our home island nether portal. This happened in another Survival world where we had separate bases and 2 Overworld nether portals, but this time both Overworld portals led to the same (nether) portal, which of course led to my friend's base. We spend at least 30 min. and 2 diamond picks (we were killed by mobs) creating more portals but all of them led to random caves below the ocean. This is so weird, and we can't travel using nether portals. --> IGNORE THE 1.16 Pre-release 2 IT WON'T LET ME POST WITHOUT IT <--