Still doesn't answer the questions, why were the kids placed where they were,
Emergency foster placement, so presumably first available people.
why was the removal initiated after the political party membership revealed
Well, supposedly it wasn't - it was because they were worried that a)the birth family would be able to find the kids or knew where they were.
b)the kids needed carers who could speak their language (which seems fair enough if you have suitable carers - which I guess is more likely in Rotherham)
are the now separated siblings in a care setting that meets the language/ cultural needs,
Hard to know as for pretty obvious reasons they can't tell you where the kids are now.
why can a social worker on the case be a member of UKIP but not the carers?
Well, it kind of turns out that they can, and maybe that the UKIP membership isn't really that relevant generally.
Having said that, whilst it seems like the main thing was a desire to find a culturally suitable placement (ie. one where the carers would know the same language as the children), and to avoid the children being found by their birth parents, you could argue that due to the local situation - large population of migrants, massive publicity in their home countries of how British social services are 'stealing their children' and taking them away from their culture, having Roma kids fostered by members of an anti-immigrant British party would actually be a bad thing, as it would further fuel all that publicity, and could have a real negative effect on the relations of council + social services with other members of the Roma community. It is perhaps more believable that people stealing children and taking them away from their home culture would include people who are members of a party that is explicitly anti multiculturalism, anti-immigration etc. And it is obviously in the interests of all Roma children, including those in this case that good relations with the social services are maintained.