How do I switch feeds? Where to start please?

[Twinsplusonesurprise]

DS 15wo has been BF since birth, no real problems apart from juggling twin DDs 2.5yo. Enough said!
I've just last week introduced a bottle so that DH can put him to bed sometimes so I can spend time with DDs.
I think I'd like to move towards bottle FF in day with BF first thing in the morning, around 7am and last thing at night, 10.30pm. He's really slipped off the loose routine we had recently but roughly feeds 7, 10.30, 2.00, split feed 5 & 6pm then 10.30. It has to be loose to fit with DDs.
How do I do this? One by one? Which first? What can I expect? Will I be able to still do those first and last feeds until he's past 6 months?

I'd start by introducing a bottle feed gradually ie a feed at a time. I started out with a bottle as part of a split feed at bedtime, then another at lunchtime and then gradually one at mid/late afternoon.

DD is now 9+ months and has 3 bottles: approximately 11ish, 4 and 7. I bf her first thing in the morning before breakfast and if she wants it again before bed. Oh and when she wakes up at night!

Hope that helps.

Ah thanks fflonki
So I'll start today by giving him 2 bottles and seeing how it goes. Is it probably best to do alternate bf and ff so that my supply doesn't plummet?

Yes I started out alternating feeds so gave her the lunchtime bottle, then bf at about 3ish, then the next bottle at about 5.30, just before her bath. But if we were out and about I gave her the second bottle at 3ish - I don't mind bf-ing in public but it's a bit of a faff as she's very unsettled in public so would pull on/off all the time so it was easier (and quicker!) to bottle feed.

Actually sometimes when we're at home now I bf her in the afternoon (especially if she's resisting sleep), and milk still comes out even if I hadn't been bf-ing in the afternoon for days, so I kinda think your boobs will still get the milk out if there's a baby attached to it! (Or maybe I'm just lucky!!)

Fab advice thanks. I gave him bottle at 10 and he's had such a good nap. The first for days poor sausage.
Like you I don't mind bf in public either but he does get so distracted and fidgets around all over the place and the feed takes an age. He's started doing that at home too. Which in itself is hard because I'm trying to watch my twin DDs who are 2.5 and kami kazi! Sadly I'm on the path to stopping which feels dreadful but it is also inevitable and part of him growing and changing I guess.
Am rambling. Thanks for your tips.