The biggest problem you'll have with taking 5 Seers *AND* 3 Wraithlords is not having many points left over for anything else - particularly those all-important Troops, which as Wraithguard/Blades are already quite expensive. Take a good hard look at the number of Wraith units that would benefit from Spirit Marks and Battle Focus, and ask yourself - do I *really* need 5? Will 3, or even 2 do?
How many points are we talking about, and what else is in the list...?
Personally, I'd think this was cool, but in a tournament setting and perhaps against others it's not likely to fly. You have a number of issues - different model size, different base size, different weapons (Seers don't get the shields...) and possible confusion with other Wraith models in the list. If it's to be accepted, you really need to pull the stops out on the modelling.