I'm no expert, but I think it will be okay because two conditions need to be met:
1. They need to provide bank statements that show that there is money in their account
2. They need to give consent that the money in the account is available for Chris's use (so he won't have to use public funds).
As for the actual syntax of the letter I think as long as it is well written and is signed then it shouldn't matter much, but it's usually better to give them too much information than not enough.