Toilet training help please

[Anomaly]

I've two Shih tzu puppies and I am really struggling with toilet training. Wees seem sorted and as long as they get out regularly they don't have many accidents. My issue is that they won't poo on the lead. Even if I take them for a walk after they have fed they just don't poo. Inevitably they end up pooing in the house. Can anyone give me any advice as to how I get them to poo on walks.

Do you have a garden? Will they poo there?

Yes they will poo in the garden but seem to prefer the kitchen. I kept them both with me nearly all day yesterday waiting for signs they needed poos. One eventually performed in the garden last night and this morning and got a big reward the other did nothing until this morning. She's since been out several times both walks and in the garden but waited until she was alone in the kitchen to go again. If need be I will have to keep them with me all the time but I'm worried they'll develop issues at being left alone then.