Confused about 8962 Shared allocation

I've read through the 8962 instructions and Pub. 974 and I'm still very confused about 8962 shared allocations.

 

Here's my situation:

I divorced in 2018.  I am required to pay health insurance for both of our kids.  I claim our daughter as dependent, my ex-spouse claims our son (50/50 custody arrangement).  My ex-spouse's income is right around 100% FPL and receives a large APTC.  My income is right around 400% FPL (household size of 2) and do not receive APTC.

 

I have so many questions, but my first question is do I need to do the shared allocation if I am eligible for a PTC? Can I just allocate 100% to my ex-spouse since she would likely getting a greater benefit than me? I have a family plan, so I don't know how to just allocate my kids' premiums.  Since my son is not on my tax return, it sucks that his premiums are not eligible for the PTC.  I am so confused, so any clarifications would be appreciated!