Welcome!
Firstly, welcome to a wonderful hobby! There is so much to learn and to love about RC planes.
Secondly, congratulations on the tranche of RC equipment. To have a trainer plane is a great start. You may want to check that the plane with the Saito FA-150 is in fact a trainer plane; that is the largest engine I've ever heard of in a trainer and one rarely finds a Saito on a trainer. I suspect it isn't a trainer, it may just look a bit like one.
You are also lucky as you have your wifes grandpa as a resource. He'll be in a good position to guide you through the equipment and get you started.
I'd ask him about the batteries. Most older batteries are not worth the risk of using; they may look fine, but they may hold 1/10th of their original charge and could lead to a safe crash if you are lucky, and much worse if you aren't. Dispose of them responsibly (Cadmium is highly toxic to the environment) and get new ones - it's completely worth it. Don't fly with untested or unknown batteries. They age poorly and are cheap to replace... so do it.
I once read here that 'the planes life expectancy is directly proportional to the owners ability to follow instruction'. I agree. Don't get 'flying fever' and ignore good reason to not fly.
Be humble. Learn from the experienced people at the field. Ask questions on here and elsewhere. You'll find there's nothing wrong with asking questions, although you may get different opinions. If two experienced people suggest different things... it likely doesn't matter as neither is a idiot.
You've got a lot to learn, but it's SO much fun!
1) Learn all you can from the internet. Forums like these are very helpful. Use the search box.
2) Buy a flight simulator as it will save you a LOT of time/money/disappointment and allow you to quickly get in the air with an instructor. Learning takes time.
3) Join a local RC club - they are full of well-informed, friendly people.
4) Join the AMA - it offers insurance and access to the best flying sites that will keep you out of trouble. The AMA is the 'voice' of our world; join and benefit from it.
5) Get any local permit to fly in designated areas (if applicable).
6) Learn about batteries, engines, tuning, propellers, servos, FM/2.4ghz, stalling, take-offs, landings, Center of Gravity issues, engine care and more.
7) Enjoy the most engaging and exciting hobby I can think of!
Keep the questions coming. If in doubt, photos will help us answer any questions.
PD.