MrsNuttella congratulations! A small gap will be lovely - maybe a bit more work in the early months, but much easier in the long term as you can do holidays/ days out/ clubs that suit both children, and won't have to wake a baby for the older one's KiGa run when he or she has only just fallen asleep at 7am after not sleeping all night, or drag a toddler along to drop off and pick an older child to all the clubs and playdates they "have" to do ... Unless, like me, you have a DC 3 when your older 2 are 5.5 and 3.5 (or in your case 5 and 4) I guess :o
Linzer that is an impressive social life!
Ambling sorry to hear about your niece, hope she was caught very early as you say and has the best possible chance of a full recovery.
C4ro glad the playdate went well. There aren't many families at our KiGa where both parents work, but somehow DS1 is attracted exclusively to friends with 2 working parents! :o DD was the opposite and had a large friendship circle with whom she had pretty much daily play arrangements, but not one of the mums worked! So it was an odd contrast with DS1, who is DC2, and starting the notes in bags thing! DD wants to go to REalschule - some children do change school after year 5 and then repeat year 5 at the higher level of school - guess she could, but she is very friend-focussed, and I have checked and discovered all the Realschule kids from our school go to the same Realschule, and all the Gymnasium kids to the same Gymnasium (they don't have to, but they are the only ones with a bus service to our villages :o ) so its likely she will have friends at both school and not want to drop down a year... She can do an extra year at the end of Realschule though - DH pointed out that even if she did an extra 2 years she wouldn't be noticeably "old" finishing school...
Inaminutenow I am very sorry for your loss. I do feel our quality of life is better in Germany, but I don't think you can really generalise about Germany as a whole can you? I don't think my experience of rural Bavaria would help somebody thinking of moving to Berlin or Saxony... or anywhere but rural Bavaria probably... so it would depend where in Germany you are thinking of moving to.
I do think once you have lived for years and years in a country other than your own, as an integrated member of the community married to a local rather than in an ex-pat situation especially, you (not just you, "one") will never feel totally at home back in your country of origin, but that it will always have a pull while you remain in your adopted country.
I don't know what I would do in your situation - I am not totally sure I would return to the UK as my in-laws are more hands on help with the kids, my own family would offer us a roof but are much less "comfortable" to be around and much less hands on. How close are you to your family and extended family? Would you be leaving very close, supportive friends in the UK? Its not an easy decision is it?
I guess the only advice would be to move before your eldest would need to go into Year 3 in the German system, in order to be settled in before year 4 when decisions about secondary are made, though the exact date for that depends on birthday and on the state you're in - some have August cut offs like the UK, but Bavaria has a 30th Sept cut off for each school year and is complicated by a lot of children being held back a year too... so your DC1 could be 8 or 9 going into Year 3. I assume your children speak German as a mother tongue and are bilingual?
Good luck with the decision, I agree you need to take at least several months deciding and weighing up the pros and cons though. If you are not working or taking some time off work to cope with your bereavement maybe you and your children could take an extended break of a couple of months near/ with your parents both for support and to see how the children like day to day life there when they aren't exactly "on holiday"... maybe most of the school summer holiday if you don't want to take them out of school?