1.对.few 本身具有否定含义,表示很少的,几乎没有.
2.我的理解是这样的：50便士的硬币和成磅的硬币.
fifty pence piece是固定表达,当说面值时用.eg.a two-cent piece 一枚二分硬币.或者是 a piece of two.
而pound coins 就是指英镑的硬币,比如1英磅,2英镑.
3.there 在此处肯定是指代作用.如果你结合这句的上下文来看,就不难发现there指代的是money box.
上下文是：My nephew,George,has a money box but it is always empty.Very few of the 50 pence pieces and pound coins I have given him have found their way there.翻译成汉语来看,就更清晰明了：我的外甥乔治有一个储蓄罐,但总是空空的.我给了不少50便士的硬币,但没有几个存到储蓄罐里.
如果觉得言之有理,found their way there就=found their way money box？但是这句话我还是不太懂，求进一步解答