for TFCD.. yes, 50mm f1.8 enough. but it cannot be used for indoor event.
for 18-50... may not be enough for indoor event, may not be enough for TFCD too.
24-70.. should be enough for both usage.
i'm using 28-75 f2.8 for portrait by the way. but for group photo for indoor event, you will need wider lens.
Frankly, if you are looking at purely events (group shots/table shots) and TFCDs.. i would think that the 17-50 (you referring to tameron?) f2.8 would be suffice.
18-200 is an all purpose lens. With proper settings, its possible to use it for events too. =)
Don't go for the ultra zooms, the IQ is really bad... unless you have an awful stigma for changing lenses. Kit lens + a 55-250 (or 55-200 if you're nikon) can easily give you double the quality at the same or lower price.
Truly speaking, 17-50 F2.8 overlaps 50mm F1.8, generally you will still stop down near F2.8 for portraits with the 50mm... that lens shouldn't be overused wide open.
As for your TFCD... I believe they're friendly photoshoots... perhaps you can consider the Tamron 28-75mm F2.8 or Sigma 30mm F1.4 (different use) otherwise, do consider asking your friends to let you explore what focal length you need. What do you have at the moment?