There is a high chance that anything that we will help you with will be obsolete in 2 weeks
For now I just focus on running big blobs of daemonettes, khorne dogs w. heralds kitted out w. grimoire (ensured by the Fateweaver). Such a powerful amount of threats never did me wrong and a daemonette blob with rending can take down any tyranid
CC monstrosity swiftly. And as an added value they are pretty difficult to get focussed down by biovores if you spread out your models all the way.
The only problem I have with nids are dual flyrants with devourers. I usually employ a slaaneshi
DP w. that whip gift. A vector + shooting with the whip = a very wounded flyrant.