you just make it part of ordinary life. as indeed it is.
you must have a reason, presumably to be near family, or becasue you think it's better for x,y or z reasons, so you just involve them in the conversation. then you can get them to help look on rightmove or whatever, then you can all go for a weekend trip to see autnie x and have a drive around, pointing out swimming pools and schools and scout halls, with you saying 'ooo, look! i wonder if you'll go to that school!' and making it all new and exciting.
bursting into tears and being overly dramatic won't help a bit. normal to be nervous about moving, but if you're moving at least in part because it will be beneficial for the family, then i don't understand why you would cry.
save the tears for when they actually do leave their schools.
2.5 hours is nothing. you can visit at the weekend if you want to. the kids will start school and make new friends and find new clubs. kids move all the time and survive.
don't whatever you do, do what my parents did. they sat us down very seriously and broached the subject of moving, very very seriously, explaining where it would be to, what it would it would mean etc etc. it was a such a serious discussion that it freaked my sister out completely and she went into meltdown, assuming because of the general tone that this was pretty kuch The End Of The World as she knew it. she threw such a hissy that my father turned down his promotion and we didn't go. he got made redundant the following year, a week before christmas.
do not give them a choice or an option. this is not a decision for children. make it light and a Good Thing and be excited at all the new opportunities. (my kids love to look on the computer to see what fab clubs there are, and to look at new schools and dance schools, swimming pools etc)
it's just moving. kids do it all the time.