Hello amandell,
Firstly, I want to make sure I understand the situation. I'm going to assume in this comment the following and if I'm wrong, please correct me so we can properly address this.
You're in a Family Share with one of your children. Your husband created a new Family Share with his Apple ID and two child Apple IDs (please ensure everyone has their own Apple ID). You are trying to join said Family Share, instead of the one you created with your one child. In other words, you're trying to leave your Family Share and join the one your husband created, but are receiving a "Family has other Members" alert / message.
Again, I want to reiterate please make sure everyone has their own Apple IDs. Including the children, you can create child account Apple IDs and properly setup parent controls and other features with Family Share and Screen Time (Just make sure they are child accounts and you and your husband have separate Apple IDs).
The "Family has other Members" alert / message, tells me that you are trying to leave a Family Share as an organizer, but there are other members within the Family Share group. You mentioned your husband created new account so I find this the most likely scenario. In the future, please change the Apple ID instead of creating a new one - Change your Apple ID - Apple Support. Moving all data associated with one Apple ID to a new one is very challenging and has to be done manually. You can change any aspect of your Apple ID and therefore is completely unnecessary to create a new Apple ID.
- Open Settings
- Tap on Family
- Tap on every family member (excluding yourself)
- Tap on Remove Name from Family
This will remove the family member from the Family Share group - Leave or remove a member from a Family Sharing group on iPhone - Apple Support.
Once everyone is removed,
- Open Settings
- Tap on Family
- Tap on Your Name
- Tap on Stop Using Family Sharing
This should disband the Family Share group.
Assuming your husband's Family Share group has six or less members and that you haven't joined/left another Family Share group earlier this year - "Remember, you can only join one family at a time, and you can only switch to a different family group once per year" - you should be able to accept an invitation.
Set up Family Sharing - Apple Support
"If you can't accept the invitation
If you can't accept the invitation, check if someone else joined a family with your Apple ID. Remember, you can only join one family at a time, and you can only switch to a different family group once per year."