I understand the current allowance is 5 non-fed trained players of which all 5 can be on the overseas quota.
On top of that any player already playing in SL when the rules changed (about 4 yrs ago) is exempt from the non-fed trained rule. As such McGoldrick doesn't count as 1 of the non-fed trained players but he still fills one of the overseas quota spots.
So I believe our position is:
Non-fed trained: Chase, Youngquest, Millington, Grehan*
Overseas quota: Chase, Youngquest, Millington, McGoldrick
* I'm presuming that with both his parents being British, Grehan has a UK passport and so doesn't count on the overseas quota.
So Cas could sign another overseas player to take up the 5th non-fed trained spot and that player could also be on the overseas quota (ie. doesn't have an EU passport and can't claim KOLPAC status)
That said, looking at the number of overseas players some other clubs seem to have (Wakey have signed no less than 6 players that last season were plying their trade in the NRL) I'm wondering whether the RFL have done a crafty expanding of the allowance once again!?