S., congrats on the baby boy. You are wondering how to encourage your baby to take a feeding from Grandma. How lucky he is that it is Grandma who will be loving him to pieces and caring for him while you are at work.
Something for you to try is to nurse him, be sure he is content, and then let her 'play' with him and his bottle. No power struggles, just a relaxed positive time of play for him. He won't be hungry, she won't be stressed out. Also, do not just stick the bottle in his mouth. He is a boy who wants a choice. Just have her pffer it to him, and let him decide. Do not worry if you can't get him to take a bottle, she can always feed him with a spoon if she is desparate. But, mostly, she can try to feed him before he wakes up. Once he is awake, he knows his momma is missing and he may cry for you...not the feeding...you the momma. It will help if she spends oodles of time with him now. Snuggling, cuddling, with no pressure to take a bottle. Just enjoying each other. Then, trying again with no stress and just let him play with it.
If you are going to be able to pump when you are away and he will be allowed to continue breastfeeding, you really should not do the bottles. Actually, ideally, he associates Grandma with a bottle and a cuddle and Momma with the breast and all the wonderful parts of being Momma. He will continue to breasteed and choose his Momma ovee the bottle every time then! And still take the bottle when he must becuase Mommma is not there.
There is a great website to check out for more information:
www.kellymom.com just put 'working' in the search browser.
Best,
P.