I need to connect my drives G drives that are Firewire 800 to my new Macbook pro

You can use the ThunderBolt-2 to FireWire-800 adapter in conjunction with a ThunderBolt-3 <-> Thunderbolt-2 adapter. Not a cheap solution, but it should work.

Do you still have the Mac with the FireWire-800 port?

If so, you could shared the drive across your Network. Slow, but the files would show up eventually.