Got my trust filled out... future questions - amendments and beneficiary

Ok so I filled out the trust through National Gun Trust, thank you all for your help on my previous post

Questions.. since this is all odd and confusing to me.

So when I do the paperwork through my dealer I give them the witnessed and notarized paperwork to send in along with application, finger prints etc...

when that is all done, do I need to amend it to add the new supressor to it or is it already on there?

What about a second, third etc..? Do I need to amend the trust every time I add an NFA item? Or only when I change person/persons (trustee, beneficiary etc..)

Lastly, I have my spouse as co trustee and beneficiary, and also my kids as beneficiary. They're underage which is why they're beneficiary only. That being said what do I put in for the percentages for leaving it to them?