I agree with the others. I have an 11 year old collie and Zoe who is a little over a year but still pretty active. I started walking them together when we first got Zoe and it really does help but I have to say that my collie just tolerates Zoe although sometimes I think she really does like her, just doesn't want to admit it.
Zoe is very submissive and I think that does help. I don't really let my two work it out themselves because Sasha is so much bigger but I think you probably could let your two work it out on their own. Zoe seems to know that she can't go crazy with Sasha but you should see her with another puppy. She's a maniac! Anyways, good luck with your babies!