I don't think you should love anyone the same as you love another person.
Instead of feeling guilty help build some love by making it a point to connect with them at least once every day they are with you. How old are they? This will only take a few minutes a day. When you first see them greet them as warmly as they will allow, and try to get some physical contact. Try to do it one on one (ie without ds or dh right in your faces too), if they won't hug then shake hands or high five and try to have a nice thing you thought about them when they were gone (I was watching ____ and though you would have liked _______).
Sure you might feel stupid if you are reaching out for a kid who isn't paying much attention, but that's part of being a stepparent (a thankless job if there ever was one) and even if the kid won't make a move back, I think many of them do appreciate it.
Another way you can connect is helping them. I think this is one of the hardest things for stepparents to do, especially if the step kids are older and can do the thing by themselves, but everyone likes to have help. Again, if you could just spend 2 minutes helping them with a chore or getting ready I think most kids really like that.
The easiest is just to stop what ever you are doing when they come to you and pay attention.
About the whining, many kids go through phases where they whine (if your dsc are about 5,6, or 7 I think that is prime time for whining). On the whole whiny and dramatic (while annoying) are relatively minor problems and you wouldn't want to force them to be respectful (that's fear not respect). I think following some of the suggestions above will work the best for increasing the kindness in the family.