can I safely charge a MacBook Pro 2016 with 49W ?

From: Find the right power adapter and cable for your Mac notebook - Apple Support

"Power adapters for Mac notebooks are available in 29W, 45W, 60W, 61W, 85W, and 87W varieties. You should use the appropriate wattage power adapter for your Mac notebook. You can use a compatible higher wattage adapter without issue, but it won't make your computer charge faster or operate differently. Lower wattage adapters don't provide enough power.

MagSafe power adapters have three pieces: Connector and adapter, AC cable, and the AC plug, or "duckhead."

MacBook (2015 and later) comes with an Apple 29W USB-C Power Adapter with duckhead and a USB-C Charge Cable. MacBook Pro (2016 and later) comes with an Apple 61W or 87W USB-C Power Adapter with duckhead and a USB-C Charge Cable."

Yes. It will take longer to charge if it gets less power than its normal charger provides.