Does someone has any suggestions how to make 17 BTC with 7 BTC starting capital in short period of time?
I think that you can try to gamble with them because that can earn you some quick Bitcoin but the chance of winning is not big so now what can happen if it goes wrong.
If you do not want to do that then you would have to use your own money.
Gambling is not a right place to multiply your coins as there is full possibility that you will loose whatever you have, it would be far better if you try your luck on trading, as you have chance of making profits and if you loose, you won't loose everything.