You can send them together and if you paid for any extra labels you can cancel them here:
https://www.ebay.co.uk/claims/simple-delivery/refund/seller
If the buyer paid for them they will be refunded automatically in 30 days. The payments for the untracked items will be released in 14 days.
The alternative would be to cancel/refund the transactions with the buyer's agreement and relist with items on one listing and a single postage cost for the buyer to buy and pay again.
