Help with lens selection.

So im shooting my first wedding in a month. It's a favor for my wife's cousin. That being said I'm planning using a rented 18-35f1.8 on my 60d, and put my 70-200 on a rented 6d. My question is whether i should consider renting 35f1.4 for the 6d as well.

Sounds like with the two you currently are planning to use your pretty well covered.

You are covered unless a lens breaks. I would get the 35 1.4 just in case.

Have a look at the wedding FAQ. The equipment list is out of date, but it's a start.

Having spare equipment is essential, even for a favor. Maybe especially then. If the 18-35 breaks then you've got a big problem. So yes you should rent the 35mm. Also make sure you have a flash and backup flash, batteries, etc.

Know you are doing it so best of luck but just a suggestion, never shoot family or friends. And if you can find a photographer doing a wedding sooner then this one, offer to tag along and carry equipment or anything for free. Watching someone who has done it before would be a big help. And of course, read everything you can on this forum about weddings.