Getting a paternity test...

My husbands ex from 10-11 years ago had a baby but told him the kid wasn’t his and he hasn’t heard anything from her since. Well yesterday he got a call from her telling him that the kid is his and she needs help because her mom is sick and stuff. Obviously he said he needed a dna test to believe it after her telling him its not his when it was born. She got pretty defensive about a dna test, which fuel my suspension that she might be lying. If the kid is his then we want a relationship and want to be there for him, but we want to be very cautious about believe her. Do we need to get a lawyer to do a paternity test?