I love seeded wholemeal bread so my question is" how much in weight of mixed seeds can I use in a large loaf in bread maker without the cut slices falling apart...???
What forumla/recipe are you using?
Without more info., I can only guess:
Start with 22% (not of total weight, but of total flour weight).
For example, if your bread contains 1000 g of flour, use 220 grams of seeds.
Seeds absorb water, so consider increasing hydration/water as you increase seed.