I'd say up to you, but would your brother allow sibling's children only? My sister did that at her wedding.

Or could you all stay in a hotel overnight close by, with your MiL babysitting in the hotel? So you can still feed to sleep and be close if you're needed?

Personally, I'd hate to miss a sibling's wedding. But then I also wouldn't leave my baby an hour away overnight when he was that small. Tough call.