Playing three games in a row from the same series is almost impossible, it happens to me too. You can beat them when you feel like it but you should! In fact if you really enjoy the series you can go and play 4 5 and 6 and so on. But don't bother with 13, that one doesn't count!
You can't say that, you don't know if he's gonna like the game or not. It's not like everybody who plays XIII hates it FOR SURE. I like it for example =P
And since you love LoD so much, I cannot imagine you not loving FFVII as well. And about playing three games back to back, if you feel like you really wanna play it, you should go for it. I was able to play pretty much the entire main series in a row once.
However, FFVIII is an odd beast. The Draw/Junction system takes a certain mindset to not get frustrating/boring. You can easily break the game, but you gotta take advantage of some GF's abilites (Mug, Refine...). If you plan on tackling the rest of the series, I'd recommend skipping it and going straight for FFIX and then go back to FFIV and make your way to VIII from that. I'd say play X, XII and XIII before VIII too =P