can't face time with multiple parties on ipad

Perhaps you need to update your iPad Air 2 to iPadOS 13.5.1.

See this support article:--> Use Group FaceTime on your iPhone, iPad, and iPod touch - Apple Support

Regards

Giulio

To use Group FaceTime video calls, you need iOS 12.1.4 or later, or iPadOS on one of these devices:

iPhone 6s or later

iPad Pro or later

iPad Air 2 or later

iPad mini 4 or later

iPad (5th generation) or later

iPod touch (7th generation)

Earlier models of iPhone, iPad, and iPod touch that support iOS 12.1.4 can join Group FaceTime calls as audio ONLY participants.

If your iPad Air 2 is still using iOS 11, you need to upgrade that iPad to the latest iPadOS with your iPad connected to a Mac or Windows PC, also connected to the Internet, running the latest version of the iTunes application for Mac or Windows PC, and use the Software Update feature of iTunes to upgrade your iPad to the latest iPadOS version.

Best of Luck to You!

No, read this paragrafh in the support article I posted:

To use Group FaceTime video calls, you need iOS 12.1.4 or later, or iPadOS on one of these devices: iPhone 6s or later, iPad Pro or later, iPad Air 2 or later, iPad mini 4 or later, iPad (5th generation) or later, or iPod touch (7th generation). Earlier models of iPhone, iPad, and iPod touch that support iOS 12.1.4 can join Group FaceTime calls as

audio participants.

Regards

Giulio

So, if the issue still persists, you should check all your settings on that iPad, according to the support guide I posted, (I repeat it here for convenience):--> Use Group FaceTime on your iPhone, iPad, and iPod touch - Apple Support

If you still can't use group FaceTime, I would contact Apple Support and explain your problem:--> Get Support

Regards

Giulio