madroid Thanks. Yes you are right, the house will only get smaller with time and we don't want to keep postponing the decision.
hellooosweetheart I appreciate that this is a 1st world problem but nevertheless it's still an issue we are facing as a family which is important for us to resolve. I also know too well that we are in a lucky position and that many people are in much more difficult situation. I have been through a lot myself, believe it or not, so we are grateful for everything we have and we have worked very hard to get here.
mum2015 Thanks. It's a tube ride (1 stop) and then walk. As I wrote, I appreciate that many parents are ok sending their children by public transport but we would rather not do that. We feel the same as you, this might be our last chance to make a move to a more long term house but the idea of such a large mortgage is scary.
sugarbum Thanks. That's what we feel more and more. If it was just a small house, we would have done the extension. But the 3 issues combined makes us leaning towards moving.
JoJoSM2 Thanks. Yes we did some enquiries and they might have to continue in their existing Primary until they get a place in the new one. Not ideal but it's not too far and manageable for a shorter period. The good news is that there are several good primaries in the new area so hopefully a higher chance that they would get in.
Your point about the higher interest rate and the pressure to have full time jobs and maintain the level of salary needed is the scary part. You never know what can happen, being it redundancy, poor health, wellbeing etc. I have first hand experience how things can change from day to the next.
Yes, 4 bed with 2 bathrooms would cost around £600k. If the issue was just the small house, we would have done the extension. In any case, we see it as a home rather than investment. However, the combined issues are making us leaning towards a move, despite the very large mortgage.