They are very unlikely to bite honestly. I've had over 30 guineas over the years and never been bitten.
I started getting my young guineas out the day after I got them. To make them less nervous, make sure they see your hands first and make slow steady movements and scoop them from underneath.
Alternatively, if you're a bit too nervous to do this and feel you risk dropping them you can always use a snuggle sack or tunnel and wait for them to go inside and lift the tunnel/ cuddle sack our with the guinea pig safely inside.
I would start by getting them out once or twice a day for literally a minute at a time then put them back. You can stroke them and give treats/ veggies whilst they're out so they begin to associate lap time with positive things. You can slowly leave them out for longer if they seem comfortable.
Quick tip: a towel over your lap is always a good idea in case of piggy accidents.