with that spesific model setup you can not play matched games(points), only open and narrative games, and that stuff is so un regulated that you need a big amount of house rules to make it even work, thats why 98% of AoS games are matched play.(or matched played house ruled with narrative games)
in matched play there is restrictions you must follow in addition to points.
for matched play, your mentioned selections would be as following:
your soulblight is 520p(provided you ment blood knight and not black knight), the NH is 480p but you have 1 stalker too mutch and 6 reapers to few.
(if you ment black knights then your mixed skelly/vamp is 380p)
in low point games (max 1000p) allied faction can be max 200p. in standard range games (1001-2000p) allies can be maximum 400p.
the rest of the army has to be the main faction, so either heavy on the nighthaunts or heavy on the soulblight.
if you can find some regular opponents and house rule inn some limitations, you can play open games with everything you and your partner wants to start with. if you want to go to a club or games workshop drop in games and play agasint random strangers, you need to make a matched play army.
so the choise is basicly up to you two. hard to give more advices before you two have discussed this further.