S.T.
i'm on a very different page from everyone else. i think it's perfectly possible to only take on as many kids as one can handle, and still be fair.
the poster is not a parent, and has already pushed her comfort zone. saying that she MUST take both girls, one of whom is a toddler (challenging for experienced parents) is a recipe for miserable weekends for everybody.
i think you should be frank with the parents that 2 little girls are too much for you to watch for an entire weekend. you're not bad for craving some one-on-one time with the child you fostered. clearly you have big hearts, and this is a cherished relationship.
i do strongly suggest that you work on developing a relationship with the little sister. not only will this balance the perception of favoritism, it will harbor sweet gifts for you.
but i think it's perfectly okay to request that you get the girls one at a time, or both together for short visits, like an afternoon. kids are not package deals. they are individuals, and are healthier and stronger for learning at young ages to develop relationships on individual bases.
khairete
S.