Does anyone have experience of educating some do privately and some in state sector?

Have you taken dc2 to look around the local comp and does he like it? Or is he under the illusion that he might be going to the outstanding state school with the other children in his class? You will probably decide within the first term or two whether the local comp is working out - you obviously have the financial means if necessary to move him into the private sector and then worry about dcs 3 and 4 later.

I had a friend who did this. Her DS went private from second year of secondary as he needed some extra support he wasn't getting in the state school. The DD was the type to thrive anywhere so she stayed in the state system. They didn't really make a big deal of it with the children, they always just explained it as being the best match school for each of them. I don't think their DCs however got to choose which school, one was more the default local state school, the private school one nearby that happened to have the right fit. Both DCs are grown up now and close as siblings and not scarred by being in different sectors whilst at school.

We've ended up doing this by accident. Both DC went to state primary initially then to a prep school which they had to attend as cathedral choristers. Chose private school on a music scholarship for DS at 13, which became an academy a year later - he's still there in 6th form. DD has gone to a private school. Both schools were the best fit for the individual child and assuming they're being honest, neither seems resentful of the other. Ultimately, your DC need to be happy with their school, and hopefully their natural academic ability will stand them both in good stead.