WooCommerce, add js-field on checkout page

Hi all, We have woo-commerce website where users can book some tennis classes (as simple products), and we just need to add the ability to add family members there to the class (on the /checkout page). So, we have created some tennis class as product already, and have made the "family members" field for the register-form: [login to view URL] (here we can attach up to 5 family members with simple js, just the name and date-of-birth for each, and save them to profile) The task is on /checkout form. 1. Let's check if some tennis class is added to cart at all. There can be other products (not tennis classes) from the shop, so, we have to mark "tennis class" products with some checkbox, or maybe make different product-type for them. Something like this. 2. If there is "tennis class" added to cart, we want to show the field with family members like this: [login to view URL] . Let's load the family members to this field from profile. Put the user's firstname and lastname to the 1st place (to "Adam Smith), and add all the family members to the right side. 3. Simple js-code to add/delete family members. 4. Save it to profile when checkout is submitted. Please let me know your terms and fixed cost! Thanks.