how do I put two bills to one payment

You can. One bank payment can settle several bills at once: a batched supplier payment, one cheque covering two invoices, a single transfer clearing a month of accounts.

Do it from the bill side:

1. Go to Ledger › Expenses
2. On an approved bill, click its purple Match pill
3. Pick the bank transaction that paid it: because that transaction is larger than the one bill, the picker opens a combine pane
4. Tick the other bills the payment covered. A running Selected total shows how much of the transaction you've allocated
5. Confirm

Talisk records a separate payment against each bill and closes them. If the bills don't add up to exactly the transaction, the last one takes a partial payment.

Three conditions: every bill must be approved first, the bank transaction has to still be unmatched, and combined payments are CAD-only: foreign-currency bills are settled one at a time. Start from the bill, not from the banking list; that side pairs one bill at a time.