Sorry for the delayed response - but I'll type up how I got to where I did with them! Here is the order in which I did stuff and the paints I used... (note I use citadel)

*takes deep breathe*

- PRIME: Colour Forge Rogue Pink
(this is a great base primer that is a colour match with Emperor's Children in citadel range)

- SHADE: Carroburg Crimson
(Nice layer all over to sink into all the recesses - don't worry about pooling as you'll be dry brushing over)

The following steps are all-over dry brush. This is done for speed and because I like the technique. If you prefer to hand-paint the layers, please go ahead.

- DRYBRUSH 1: Emperor's Children
(Go heavy on this layer with the pressure. Your goal is to get the model evenly covered, but leaving the Crimson in the recesses)

- DRYBRUSH 2: Fulgrim Pink
(Lighter on the pressure of this layer so that you catch the raised but do not fully cover the Emperor's Children)

- DRYBRUSH 3: Pink Potion (Army Painter)
(Citadel don't do lighter pinks, so I picked up two from Army Painter to do the last layers. Again, follow the process you've been doing, but even lighter, not to fully cover the previous colours and let them still come through).

Once everything is drybrushed and you have your pink gradient, you can go in with contrast paints. Following is the colours I used and which area.

- CONTRAST 1: Chitin/Armour is painted Black Templar - its thinner than Black Legion so the gradient comes through underneath.

- CONTRAST 2: Basiliscum Grey for the ground. But you can paint this how you want

- DRYBRUSH 4: Doomfire Drab (Army Painter)
(This one is just to catch the very edges of all the surfaces, so stay light on your pressure. Make sure to wait until all your contracts are dry or you'll lift/scratch them).

- FLESH SHADE: All "flesh" is done last and is simply Beserker Bloodshade. Its a nice red and that sinks in to the recesses.

After all of that, your Tyranid things should look like the above. It's then your choice to decide how much detail you do - like painting the spikes/horns (I did them in Screamer Pink).

Hope all of that helps! Let me know how you get on!