Answer:
$480,000
Step-by-step explanation:
The Federal gift tax annual exclusion is $15,000 per person. Since they are gift splitting, they can give up to $30,000 per person. The limit is imposed by the couple's total lifetime exclusion which is $11.58 million for 2020. This means that you can make gifts to multiple people during your lifetime and if the total gifts do not pass the lifetime exclusion, you will not be taxed for it.
5 children x 2 (their spouses) = 10 people
6 grandchildren
total = 16 people
total annual gifts = 16 x $30,000 = $480,000