Unless you are afraid that the baby will be molested, or that the in-laws have a disease, what's the problem?
Was this rule initiated by you or your husband?
Some families don't get close, and don't even kiss their own children which is hard for me to understand - love should be shown and felt, not just assumed.
What are you really scared of? IF it is related to something in the past - work on it.
If it's because you fear kisses and closeness yourselves - work on it.
There will be a lot more things for you to 'protect' your child from in the future, but it does have to learn and experience love from parents and grandparents. Most children raised in a 'cold' family look for love at an early age and in the wrong place - think about it.
Good luck. I hope you get over your fears somehow.

Over-protecting is not a good thing either. We have to find a happy place in between. Happy Parenting!