Can a songwriter allow their songs to be used by another bands, and she can still perform the songs by herself (her own band)?

Let’s suppose I have 5 songs,
and two bands’ friends of mine want to use (& re-arrange, & include into their debut album) 2 of my songs,
then is it okay for me to just allow them to use my songs?
and moreover, since they’re still indie/DIY band, is it wise for me to start talking about the royalty that I will/should receive from the songs, and some legal, music-business stuff? what is/are the most important things to tell them though?

And also, since i’m the songwriter, can I also freely use those 2 songs of mine in MY band/music project?
and even to send them to a TV commercial or jingle stuff, if they’re asking for it?

what are the ‘limitations’ or ‘borders’ (or “legal border”) in all this stuff, especially for me as a songwriter myself?