4 - 5 hours to go from a Tomahawk to a PA28 seems a little OTT to me too, especially as you've already got a reasonable no. of hours total
Also I see no reason why you can't have anyone in the back - I did parts of my PPL with another student in the back (admittedly a 172 not a PA28), swapping over after an hour or two but that was with me and them as students!
Try calling somewhere else if I were you. After all, it's your money.