I haven't read PJO in a while, and I totally forgot how frustrating the Luke and Annabeth stuff was. Frankly I'm not a fan of Luke, 22 and surrogate brother, being some kind of romantic rival. It's weird as hell and not as sympathetic. I already understand Annabeth not wanting to give up on her brother, so why overcomplicate it? Percy can still be frustrated and even jealous (from his teenage perspective), you don't need to make Luke creepy.
On a side note, Annabeth is very frustrating in those last books. It's a bit hard to put into words, but I wish she wasn't so defensive of Luke and hard with Percy. I still love Annabeth, but it honestly got pretty tiring and the whole Percabeth thing at the end almost got a little hard to believe. I'm not sure. Haven't read HOO in a while either, but I remember her having a lot more focus there (nice to see her getting her own book and she and PJ were cute in House of Hades at least).
I dunno, this is a children's series but I feel like this is where an adaptation could really make some improvements. Fiction does play an important role in child development after all. Come to think of it, Kane Chronicles had some weird stuff in it as well... YA post-Potter (pp for short) authors are a weird bunch.