A couple things to consider:
1) Ensure you have an idea of highest and best use (probably retail it sounds like) for your grandfather's property - this could be very important as it relates to the location of the sewer easement so as not to restrict or complicate future development (maybe in the back of the property so that your neighbor would not be digging up your parking lot when a repair or upgrade is needed);
2) Only grant an easement the necessary size required - 25 feet seems excessive unless that's required by state or city ordinance;
3) Make sure your grandfather is adequately compensated for you and his time to get this done. While it does appears there is mutual benefit, it customarily comes with a price to be deeded, and you have that leverage since this neighbor needs it now.
4) Consider the need for any other utilities that may need extension over there along the same easement and their suitability as far as location is concerned. It would be less than ideal to have one easement in the back but then be forced to have another in the front because you didn't consider another service.
Keep us posted.