Passport application for 2 children. How to send ILR BRP?

I am applying for passport of 2 British Born children. I have received the naturalization certificate for both children. I currently have ILR. The HMPO asks for the ILR and parents passport to be sent with application. I wanted to ask

1) Do I need to submit both ILR AND passport or just ILR brp is enough?

2) I am making passport application for two children so I can only send my ILR/passport with one application. Do I include a cover letter explaining this? any tips?

If the children have been registered and have an certificate of registration, you do NOT need to send the ILR BRP card for the passport (this is for those born after a parent received ILR).