how to stream two raycon earbuds symutaniously on one iphone with an iPhone SE 2021 phone

Audio sharing is only available using AirPods and certain Beats headphones.

Share audio with your wireless headphones - Apple Support

Compatible headphone models

• AirPods Max
• AirPods Pro (1st generation) and later
• AirPods (1st generation) and later
• Powerbeats
• Solo Pro
• Powerbeats Pro
• Powerbeats3 Wireless
• Beats Solo3 Wireless
• Beats Studio3 Wireless
• BeatsX
• Beats Flex
• Beats Fit Pro

Compatible iPhone, iPad, and iPod touch models

• iPhone 8 and later
• iPad Pro 12.9-inch (2nd generation) and later
• iPad Pro 11-inch
• iPad Pro 10.5-inch
• iPad Air (3rd generation) and later
• iPad mini (5th generation) and later
• iPad (5th generation) and later
• iPod touch (7th generation)

Unless the Raycon earbuds are designed to be used simultaneously, you cannot use two Bluetooth devices at the same time.

Sounds like you need to purchase earbuds which feature multipoint pairing, which your Raycon's don't support.