How do you share some feedback about certain things to your peers?

A little context.

Within our team, me and another person are two senior folks and we are the ones who are answering all the queries to external teams, product, issues, incidents. Obviously we are seniors so we tend to lead by example and try to handle as much as we can. But this is giving the junior folks a nice getaway to not pitch in and scale and handle things as well. They are happy to sit back and when me or the other senior person is not available, their response to all the queries is that we dont know because we havent worked on it and then when we come back, we respond to those.

Also for the work, what usually should take 1-2 days, takes 3-5 days for these guys. 3-5 days of work gets delivered by them in 2-3 weeks. And the reason again, this is new, i didnt not get this and i have facing this issue. In all of this, our lead is quite laid back as well and doesnt inquire more about why things are constant getting delayed from their side.

The side effect of this has been that more critical and time sensitive things gets pushed to us senior folks even more and we are seriously getting bogged down by the amount of work.

We want to question and point out to these junior folks that they need to scale up, but we feel a little helpless since it might make them more hostile and retaliate. Why are we saying these when our lead is not saying anything. That will be their argument. Plus it will create an unpleasant working environment which we dont want either.

We think of talking to our lead, but again, I am not sure if that would be considered as bitching about them.