i have a thought... does he need his "own" room or would he be comfortable sharing w/some of your girls? if he can share, it might behoove you to price him and two girls as one ressie and you/dh/two girls on the other... i'm assuming you/dh/girls would need two rooms at all-stars anyway, no?
also, if he really wants to go and money is a problem, perhaps you and dh can pitch in towards poppy's fare, or ask your sibs (if you have any) to give him his plane tix for father's day...
good luck, and i feel your pain... we soooo want my folks to join us, but mom just doesn't want the "work" that comes along w/going on vacation (packing, unpacking, and taking care of my dad away from home -- he's 87 and has some typical aging medical problems) 'cause it won't be a "vacation" for her (or so she says! LOL!)