Nursery Families are very rare, some sets rarer than others. They are valuable but because not a lot of people collect Lil Litters and even fewer extend to collect Nursery Families, so they aren't the easiest thing to sell. The people who want them, are usually willing to pay a significant amount for them however.
The Sweet Dreams Poodle and Perky Persians are easily the hardest the find and therefore, most expensive. The Sudsy Angora is probably the next hardest to find. After that the Funtime Spaniels.
The Sleepy Time Siamese and Scrub-a-dub Spaniels appear the most frequently on eBay it seems, but over all, still rare.
Prices vary a great deal. It depends on the demand. I've paid anywhere between $25 and $130 for one baby.
For this set, $65 is a fair price per baby. It's a fair middle range price that doesn't make either the seller or buyer feel ripped off. The mom depending on how that sun fading goes, is maybe $45-$50. I assume you are selling them as a set, so I personally would let all 3 go at once for $160.
Hope that helps!