Bank Statements and the Standard Visitor Visa

I am applying for a visa for my son, not for myself. I am a British citizen, whilst my son is Bolivian. I work as a missionary with special needs kids, and my income is not a lot. It's adequate for Bolivia (more than, actually) but low for the UK.

My bank statements aren't great, we've been living off savings for the past year. Additionally, there's a lot of robbery here, so I put all my money into a savings account that can't be access offline, and transfer it only when necessary. So when I get income, I pull it out of the account immediately and put it in savings. But there is obviously also a lot coming out of savings. I do it for safety reasons, but it doesn't look good when I'm trying to prove financial stability.

I also have an account with the mission here in Bolivia (and it is a registered charity in the UK) which looks way better financially, because only my rent comes out of it and it's built up a considerable amount of money over the past year. However, it's not a bank account, just an account with the mission.

So my question is, do I send my own bank accounts? Or do I have my mum, his grandmother, sponsor his visit? We will both be living with her, and she's happy to do so. But I on my other post it was suggested that the application is stronger if it isn't sponsored.

And if I were to send my own bank statements, would it help his case to state that I intend to work while in the UK? I am a registered teacher in Northern Ireland and I am registered to substitute teach.