It is not obligatory on daughters-in-law to serve their husband's family, but it is good to do things which help your husband to be a good son for his parents as much as can. Kindness is always good but Islam does allows insulting or hurting others under any circumstances. Be kind as much as you can and remember the reward of kindness as well as the results in this life as every daughter-in-law will be a mother-in-law in the future.
Wassalam.