Can the court give custody of the eldest child to the father and the youngest to the mother?

Yes; the court weighs the welfare of each child separately. Act 303 s.86(4) says that where there are two or more children of a marriage, the court is not bound to place them all in the custody of the same person, but must consider the welfare of each independently. Factors such as age, sex, schooling, health and the wishes of a child able to express an opinion are all weighed. Still, separating siblings has its own effects, so many parents arrange frequent meetings between them. The Prophet ﷺ said: “Be conscious of Allah and act justly among your children” (Sahih al-Bukhari 2587). See Hadhanah & lineage.