I had duplicated several Allays (6) and they were inside my home at my spawn with no way to escape. I left my home and entered my portal (which is next to my home) and when I arrived in the Nether all my Allays were there flying about! I re-entered the portal to go back to the overworld. Two Allays followed me thru the portal and there were none left in my house. Very strange - apparently they are able to fly thru walls...