Hello Tony and Pat.Agony aunt eh? wow the responsibility!!
Sorry,i have been at work all weekend and we had company last night so only just found your message.You may be excited now Tony.Been there got the teeshirt,seen the DVD etc.You wait till you're 10 years down the line,and you are wishing there was a contraceptive pill for fish like i do.
Anyway far be it from me to put a dampener on things!! i sometimes get a badly damaged female out of this ardent activity,and They are generally too injured to save.Be thankful she got away and leave her as long as you can to have a rest.
Yes,i have found that goldfish of mixed species will interbreed,sometimes at quite a young age,as you have discovered.It is very common for goldfish and rudd,and you will never stop the others from eating the eggs and fry.All you can do is provide plenty of cover and a few will hopefully survive.Perhaps you could put the fry,and the eggs,if you find some,into the middle section,then you can feed them special fry food.I would not be tempted to put them into a tank.I have saved some this way but it is a difficult job,and they often die,usually due to water quality going downhill through overfeeding.
Do keep us posted!!