Your u-joints are "permanently sealed" (meaning they'll eventually just fail and have to be replaced

). The gimbal bearing should be greased, you'll find the nipple on the starboard side of the transom shield, in a recess. Best to lube while the engine is running (the drive shafts/ujoints are turning anytime the engine is running, doesn't have to be in gear). Give it a few pumps, if you encounter resistance, STOP as you don't want to blow out the grease seal.
Engine oil change if it hasn't been done, drive lube change if it hasn't been done. Find your drive's dipstick and check the fluid level and condition, make sure it's not milky (evidence of water intrusion).
I'll give a big +1 to TX on keeping this fun for the family, as soon as you get stressed enough for it to turn into a battle you'll lose!

But I'll disagree and say that to do any real maintenance you need to be able to put the boat on a set of muffs and run it in your driveway. Get GOOD muffs and have LOTS of water pressure running to them. Good muffs deliver water to both sides, not just one, and have big enough water passages to not restrict the flow to the drive.