1.Would it be possible to produce a child who has 48 chromosome?
Yes it is possible. Having extra chromosomes is a result of meiotic non disjunction. This is when during meiosis homologous chromosomes fail to segregate. If one of the gametes has an extra chromosome the resulting offspring would have 47 chromosomes. This is a trisomy. Having two extra chromosomes is even rarer and is called a tetrasomy. One such possibility is the male genotype XXXY. This is an abnormality of the sex chromosomes. Normally a female would have the genotype XX while a male would have XY.
Tetrasomy is not limited theses chromosome. Autosomes can be involved. Some autosomes which have exhibited tetrasomy tendencies includes 18, 21, and 9.