Hi, there,

This isn't a breastfeeding problem - it's a sleeping problem. it's nothing you created (just in case you are thinking that) At this age it isn't advisable to start a bottle - it's the time when the usual recommendations are to wean from the bottle - it is just setting up a problem that you will have to solve further down the track.
It's generally accepted that it's the father's role to teach a baby that food and comfort are not always related. Your son is capable of learning that when he is with mummy he can breastfeed to sleep but with daddy or grandma there are other ways of getting to sleep - and this is your dp's job - not yours! You are at work.
Dad and grandma need to get more creative. Give him some time to wind down with a story - a walk in the baby sling will d0 it just about every time. A walk in a pram, a drive around the block in the car, lying down in bed or on the couch with your little one.