The genes in angels are in pairs so it sounds as though your black has a single black, single striped, single veil tail and if it has a blotchy pattern it may have a single marble gene. I would try to cross it to a gold with double veil tail genes.
I don't know what a platinum is so can't help you there.
In my view the safest way to raise angel fry is to remove the eggs and hatch and raise them seperately.