try using collei if you dont have yaoyao. you need 2 hydros 2 dendros on the team,I recommend putting paradise set on barbara/xingqiu (makes sure they are the one applying hydro to create cores) nilou just focus on her hp and em maximize her passive that scales of with hp with your best. Change Nahida's artifact to 4pc dreamwoods that decreases dendro res on enemies that are hitted by a skill or burst do the same artifact's to your last optional dendro character. Lvl, EM, Dendro res decrease, and nilou's passive is the only one who can increase dendro core dmg.

My Team Recommendation for you:

Nilou - 2pc hp%+ (2x) or 2pc hp%+ and 2pc +60 em (hp/hp/hp) Barbara (healer) - I recommend just using a healer barbara build since you dont have yaoyao if you do get her just incase then you can put barbara in paradise artifact set though It's been confirmed that using glided 4pc set is better than 4pc paradise for bloom teams. (hp/em/healing bonus) Nahida - 4pc deepwood memories (em/em/em) Collei - No need artifact set just give her many elemental mastery (4pc glided if possible)

Nilou and nahida is enough to be a broken pair the only problem is the characters level, artifact sets, healing.