Keegan and Hughes, both Irish, agreed contracts two weeks ago but the moves were held up by complications with the paperwork due to the international nature of their moves.
The pair have signed one-year contracts, with the option of a further year in the club's favour next summer.
Newey has spent the whole of pre-season with the Iron on trial, earning himself a one-year deal after impressing in friendlies.
He worked with Knill at Rotherham and is capable of playing all along the back four - which could prove vital wiith Callum Kennedy, Paul Reid and David Mirfin all missing recent pre-season games through injury.
Source: FOOTYMAD
