orphaned mouse constipated

Question
I found two orphaned mice about 5 days old. Their mother was found dead in the garage, and I heard sqeaking, and turned over the garage until I found the critters. I've had them now 3 to 4 days, and have been good about feeding (kitten formula) and rubbing their little bellies until last night....my sleep deprived brain wasn't working and I didn't help them poo after I fed them. Today, I've been rubbing their bellies and nothing. I give them a little break and try again... nothing. Is there anything I can mix into the formula to help them go? I even watered down the formula extra today....nothing. I'm afraid they won't make it if I can't get them to go SOON... but I don't want to hurt them either by rubbing too much.

Also, two days ago, when I was feeding/rubbing bellies, one of them latched on to the other's shoulder. The first time I thought he was confused, but the second time I got online and thought he might feel threatened when I rub his belly (he hates it) and his survival mode is telling him to eat his sibling. I think the other's arm might be injured, but he's using it like it doesn't hurt. Do you think I'm right to keep them separated?  Now instead of biting his sibling, he just bites my shirt or the towel (or my hand). What can I do to make him feel less threatened when I rub his belly? It seems that kind of stress could be nothing but bad news for his health.

Thank you,
Andrea

Answer
First off I would suggest going through all of my previously answered questions for information on care and feeding of orphaned baby mice. You will find some great information from my previous posts. Rubbing their bellies usually does not cause them to go to the bathroom. You will need to stimulate them by rubbing their genital area with a warm, wet cotton ball.

Most babies suckle on each other. This is very normal behavior. However, sometimes it can get out of control and too much suckling on each other can cause irritation. You usually don't have to worry too much about this unless it is done to the genitals. I highly doubt the other mouse is injured, nor do I think he was trying to eat his sibling. He is just hungry and trying to express that by latching on to anything he can. If after reading my previous posts in regards to baby mice care and you are additional questions please feel free to ask. :)