[mandco]

I would send copies of the letters now just to be on the safe side

DWP have currently suspended all face to face meetings so its unlikely that you will get a date for your appeal anytime soon if you need to attend.
I know sdd had to attend her appeal but it was really a long wait for the hearing- they went over all the paperwork and she had to give a statement of why she felt gdd qualified and how her needs affected their day to day life. It was worth it as the judge overturned the ruling awarded her dla at the high rate and backdated it to the original claim date.

Goodluck