Passenger Liner in convoys: No. Not realistic.
They generaly sailed alone and on a straight course, without zig zagging.
Good luck trying to bag one of The Great Atlantic Liners.
There was no naval escort that could keep up with them.
30+ knots ALL THE WAY. I met one once, and he almost ran us over before my guys even saw him. There was no time to do anything but get out of his way. I wanted him, but there was no way I was getting him. He was too close for a torpedo . . .then he was gone.
I have to hand it to SH3, the whole encounter was pretty realistic and super tense.
Hospital Ships are, of course, off the menu. Something one might want to think about before sinking one is that they did stop to pick up survivors, from both sides. One of those survivors might one day be you or me.

Weren't the Titanic sister ships Olympic and Britannic impressed into Wartime service? I seem to remember one was converted into a hospital ship and either this or the other struck a mine?

Yes but in WW1
Britannic was sunk by a mine and Olimpic survived to be scrapped in the 1930's

apparently Britannic may well not have sunk had all the nurses not insisted on having all the port holes open to air the wards. the water rushed in through these open port holes into the wards.