If your friends want to learn to play bridge for free, get them to download for free Learn To Play Bridge 1 from web3.acbl.org/internet/websiteForms.nsf/ltpbForm?OpenForm.
Ignore any requests for ACBL Rego numbers or similar as you do so. You can also download LTPB2 (more advanced stuff, including basic conventions) from the same site. The main website is www.acbl.org which provides this high quality free software.
The most popular place to play bridge online for free is www.bridegbase.com. If you download their software (free and safe), then under “Explore Bridge” you will find that it includes the free LTPB1 and LTPB2 software referred to in the previous paragraph.
to Play Bridge - American Contract Bridge League
What is Bridge? by Ron Klinger
"Children and Bridge" - article by David Lusk
Training Papers - used by the French International Teams for Training purposes.