Can Dependents file an extension for H4, while my H1B extension is in progress

Currently, my H1B visa is going to be expired on 30th Sep 2017 and few days my back , got the stamping done for my wife and kid and they also got the visa till 30th Sep 2017. Now , I am starting extension process for me.

They are going to travel on June 26th ,so wanted to check if there is any problem for them during their transit if new extension is filed and they are travelling on existing visa which is valid till 30th Sep 2017.

Also while my H1B extension is in progress, can I apply H4 extension for my dependents?