I have 3 accounts, without seed phrase, only address, view key and spend key. How can I check my balance? Maybe I can integrate the accounts with the wallet RPC? I think it`s possible, because xmrwallet and MyMonero work with only this data. But how?
You can restore a wallet (e.g. create a new one) with your existing address and keys. See the guide: https://www.getmonero.org/resources/user-guides/restore_from_keys.html
Once you've restored your wallet you'll be able to scan the blockchain to check your balance.
If you really want to do this via the wallet RPC, see: generate_from_keys.