when u mentioned blockchain api, it only caters to BTC only right? Any other API that is more flexible in terms of supporting more coins?
i know they also have ETH wallet but i don't know whether their API supports it also or not.
you can always use ShapeShift API though.
https://info.shapeshift.io/ it is not a wallet but it is a good service to change cryptos fast and easy. you can still receive everything in bitcoin but accept altcoins through ShapeShift. the user pays the altcoin, the site changes that to bitcoin and gives it to you.