danios are very playful and outgoing fish so most likely they are trying to get them to play, just keep an eye on them and if the swords and platties fins start to get ragged remove the danios, but like I said danios have big personalities and will try to make fish play with them, a lot of people will put them in tanks if their fish are shy because danios can bring out the playful side of almost anything. keep us posted on their progress.