If you don't have adequate clearance now, the fenders will make it worse. Sometimes the fit of the fenders seem like they won't fit - you just need to try. The only place where you might need to trim the fender is if your front fork really is that narrow not to accept the fender through it.

Mount the front fender in front of the fork and push it up all the way to get max clearance. The leftover tab will most likely need to be smashed back down to clear the headtube unless you've spaced it out. Some fender sets have pre-trimmed front fork sections designed for tight clerances - which yours does not have. Be careful if you are going to trim it. Too much and it'll be a floppy wet noodle.