It’s pretty hard to say from the information provided but it is possible that they were planted too deep.
Burying tpp deep or piling mulch up against the bark of the tree hinders the flow of moisture and nutrients from the roots up the the branches and leaves above, slowly strangling the tree.. Trees may survive a few years but this often kills them eventually. It is the most common cause of death for landscape trees and shrubs…human error.
The grass is likey browning due to dryness as it is competing with the tree for whatever moisture is available.
Of course it could also be any number of other problems but, without more information, it is all I can offer.
It would probably be a good idea to have a certified arborist come and take a look. You can locate one here: https://nysarborists.com/for-everyone/find-an-arborist