give me an idea for budgeting

Hi. my inlaws are visiting us soon. since we are on a budget and also expecting quite a few expenses ahead for my pregnancy, can someone give an idea what should be our minimum or optimum budget for bringing them including airfare,insurance,grocery and all other things that I may be missing for their 3-4 months stay?
and how much household expenses are likely to be increased on an average after the baby is born.Since we both are quite inexperienced and don't have any guidance,wanting some guideline to understand if we need to plan accordingly for more conservative savings.
thanks