The MGM Grand and the Marriott Grand Chateau are two very different types of properties. The MGM is a full service resort with numerous dining, drinking options and one of the largest casinos on The Strip. It is a place that you really wouldn’t need to leave to get the full Vegas experience. The same can be said for almost any of the Strip resorts. Marriott Grand Chateau is a timeshare property, so you will find that onsite amenities are much lesser. For example MGM has one of the largest pool complexes in Las Vegas, along with a day club Wet Republic. Marriott GC will have a pool but it will be more like a regular hotel pool.
The MGM rooms will be more luxurious as well. Bascially MGM is a property you can really only experience in Las Vegas. The Marriott, while being very nice, I know I have stayed in many Marriotts, can be found in almost any city in America. Here is a link to the Skyline Marquee Suite I mentioned. https://www.mgmgrand.com/en/hotel/skyline-marquee-suite.html
If you look at both side by side, you will see how the suites are marketed towards different travelers. I will say the one plus of the Marriott is the kitchen, but ultimately I doubt you would be cooking much while in Vegas. The kitchens are there primarily for timeshare guests as many are families who do like to cook their own meals.
A good compromise for you might be The Signature at MGM. These three towers are condo hotels. Many of the rooms/suites have balconies. You could get a few Deluxe Suites which are approx 550 sq/ft and feature a king bed and a queen sofa bed and then an approx 950 sq/ft 1 Bedroom Balcony Suite for your party. This suite will have a kitchen, if that matters. Guests of The Signature have their own pool, plus get free access to MGM Grand’s huge pool. You are about a 5-10 minute walk, depending on which tower you are in to the MGM Grand. The walk is indoors, some of it has moving sidewalks.
https://www.signaturemgmgrand.com/en.html
Another option would be Luxor. Like MGM it is a full service resort. https://www.luxor.com/en.html
You could book several Tower Deluxe Queen rooms and one Deluxe Tower Premier Suite to hold your party in. The Deluxe Tower Premier is approx 1,200 sq/ft with floor to ceiling windows. It is clocking in around $141-$285 per night plus tax and resort fee.
Plus, by booking with MGM you can take advantage of Mlife Rewards, which provides line passes, comps, and other things after you spend/gamble enough. Staying at an MGM property also allows you to room charge from any other MGM property. A nice feature vs having to hand over your credit card all the time.
I hope this was of help. Please let me know if you have any more questions.