Being a huge Palace fan and finally buying into the membership a few years ago, nope, there are no other resort chains/brands I would recommend. We had stayed at a few others, but once we tried Palace, we were sold.
Playacar Palace is beautiful, the beach is great, we were by there this past summer when they had a 200+ person wedding - it was gorgeous with the reception on the open air terrace overlooking the pool dnd beach - it really was beautiful. It is not as large a resort or have as many options for dining and entertainment as Moon or Beach, but it is beautiful and steps from all Playa Del Carmen has to offer also. Plus, you can take the ferry across to Cozumel for the day - and if you book through a member, you can visit Cozumel Palace included.
Personally though - for a large family group with kids - Moon would be my first choice - so many things to do and places to eat, etc right at the resort.
Another option may be Hard Rock Cancun - it is formerly a Palace Resort, but the brands split in the last 2 years and Cancun Palace became HR Cancun. It is in a great location, beautiful resort, quite large, great kids clubs and activities, great beach, beautiful pool - I love the improvements there and great dining choices. Same excellent service as Palace, just now with a more rock theme- worth checking on too.
Enjoy and congrats, wherever you choose!