IMHO, chances are 90% you will have problems because the tank's so small. In a larger tank, like 1000 gal and bigger, they would be quite fine, chances are. All in all it is always a gamble but the chances must be taken into account. Be prepared to separate if one will bite the other.
RTC are said to be territorial only up to a few inches, then they relax, but this is in large enough tanks. 5' tank for two 10" RTC is too small - they will be in each others face too often, especially at night - this time of day should be your main worry.