Question

there are four children in our family. my sister is Florens . 1-elder , 2-older, 3-, 4 - the oldest​

Answer 1

Ответ: elder.
Правило: Слово elder как правило используется, когда речь идет о двух детях в одной семье: Мой старший (elder) сын работает за границей. Джейн была старшей (elder) из двух сестер.

Answer 2

Based on the information you provided, the birth order of the four children in your family is as follows:

1. The oldest child (not specified whether a sister or brother)
2. Florens (your sister, who is the oldest of the siblings)
3. A child (order not specified)
4. An older child (order not specified, but younger than Florens)

It seems that the order of the third and fourth children in the family is not explicitly mentioned.