You ask a very good question and one which does not entirely have a clearly defined answer.
Technically the Surinder Singh caselaw mentions only spouse.
Now that does not mean a UK citizen excercising EU treaty rights cannot bring their non-EEA spouse into UK. It means that there is risk that UKBA may get crusty about Family Permits.
However, as I mentioned in my reply to blackcat it's not always necessary to have a UK Family Permit in order to gain legal entry to UK.
If you are prepared/able to live and work in the EU with your family for sufficient time to secure full residence cards for all, then there is a chance that you could also secure all other documentation to enable UK entry.
Do be aware though, that there's always a risk there could be denied UK entry for some reason or other.
I don't know your planned timescales but maybe you have some time to hold fast and wait and see what the results of the UKBA review of income thresholds might be.
The EU outside of UK will eventually accept a relationship of unmarried 'partner' .
Here is the definition of "The partner with whom the Union citizen has a durable relationship, duly attested of " :-
You'd need to share a lot more information on your EU plan to be able to get a better idea though.This category covers all other long term “durable” partnerships, including both opposite-sex and same-sex relationships.There is no official definition of how long the relationship must have existed. Some countries expect to see two years of living together, but if you have a child with somebody and live with them it would clearly be incompatible with the Directive to require two years of relationship history.When a member-state does not recognize civil partnerships as equivalent to marriage, this is the category which is used for entry.
Can you wait a bit and see how The Home Office will finally decide on this income threshold?
It may work in everyone's favour. We all have our fingers crossed on that.
Stay in touch on this topic and let's find the best option for you.