Hard to place children are regularly 'advertised' to people already going through the adoption process by magazines such as 'Be My Parent' and 'Children Who Wait'.
What is interesting in this case is that they have said you don't need to be an approved adopter to enquire. This strikes me as a) these children are very hard to place so they have to set the net wide, and b) potentially they have other sibling groups too, so advertising for one group may flush out others who may be suitable for other groups.
These girls will be very hard to place even without knowing details: 3 of them close in age, plus eldest is 5 and with delay. This may well be a last ditch attempt to keep the girls together. Otherwise it is likely they will consider splitting into a 1 and a 2.
However, they will need more than All they need is love, care and structure and to be together