Yes, you are completely right about this. And I can figure it out how to make them working without problem.
BUT: I keep on external drive for a simple raison: secure and encrypted. As have 1T space, can hold as today size if block chain, 5 different bitcoincore.
Or other way is to merge all wallets, what I was trying already, but without any success. Exported by dumpwallet, and got only error messages and the main wallet.dat intact and same size.
If you run it but use the -prune command when it starts, then you'll only have about 5GB of space being taken up by each blockchain as it keeps only the most recent blocks. Then you could run this with all four running.