Hi,
If you know for sure that these lumps are fibroadenomas,then you can proceed with your plans for pregnancy.
To answer your question,yes these benign breast lumps can increase in size during pregnancy and lactation,this is quite normal and nothing to worry about and you should have no problem if you intend to breast feed your baby.
Enlarged fibroadenomas can be removed but they usually tend to shrink after cessation of lactation,so if their removal is necessary,it should be delayed until hormonal status returns to normal, and a smaller excision can be performed.
Wishing you an uneventful pregnancy and delivery and a beautiful healthy baby! :)