My 3 are similar ages:3.5 DS1,in high back booster,DS2,2,in maxi-cosi tobii ,and newborn in Maxi cosi cabriofix.Spent ages looking at cars.Narrowed it down to VW Touran,Seat Alhambra,VW Sharan,SMax.In the end bought Ford S-Max.Will fit all your seats (is 7 seater) but isn't too big,v easy to drive/turn /park and has parking sensors.You should be able to pick up 2nd hand one with your budget.
DS3 due in July. DS1 aged 4 and DS2 aged 2. Both currently in Kiddy seats. Car is Freelander. Infant carrier won't fit between Kiddy seats, need new car. Live in area with free for all residents parking and even with parking sensors will be even more of a nightmare than it is at the moment if we get anything longer than our Freelander (4.5m). Really really really do not want people carrier. Have got two different infant carriers (one normal seatbelt fastened type) and one just acquired maxi Cosi with that easi fix base thing with the leg. Our original seat will fit in the middle of a Freelander 2 between the two Kiddy seats but I am not sure the Maxi Cosi base will and will never be able to do seat belt up round other seat so kinda useless. Cannot bear revisiting traumatic trip to Landrover garage with kids plus seats to try Maxi Cosi in Freelander 2. We've got about £12k to spend inc trade in on existing. Must have parking sensors and local oik proof electric folding mirrors. Would almost consider heated front seats essential. Anyone got any marvellous ideas as to what car might suit/fit our car seat combo?