A shared residency order means that the children will spend equal amounts of time living with each parent. Therefore they will have equal rights over the children - if your partners ex-husband does not agree to holidays you would have to abide by his decision. Why not organise this into the agreement by suggesting that you may want to take the children for a long holiday and theat he would still be entitled to the same amount of time at a later date. Unless it is really nasty there is no reason not to come to amicable arrangements.