there's nothing wrong with it. you're just not getting other types of families. if you don't want to get the blended family, try one of the following (some can only be gotten on the next generation)
mame family: get mametchi, then marry chantotchi with 100% bonding.
meme family: get memetchi, then marry mumutchi with 100% bonding.
kutchipa family: get kutchipatchi, then marry yonepatchi with 100% bonding.
space family: either marry your tama to sunnytchi (planetchi will sometimes show up on the dating show with him/her) or marry your tama to another tamagotchi on a famitama. there will always be one egg.
and for the neglect care families (these are bad families, but they're not the blended family)
large family: overfeed them 5 times.
ninja family: neglect the happy points 5 times.
petite family: neglect the hunger points 5 times.