Well, I can't find a good match for the other children in 1901, unfortunately.
Tracing Joshua the elder back, I see him in 1881 with his wife Ann and the following children:
Ann age 6 b. Over Darwen
Joshua age 9 b. Over Darwen
Thurston Findley age 12 b. Over Darwen.
The reference is RG11/4208 104 12 - you can look it up for free at either
www.familysearch.org or
www.ancestry.co.uk We could imagine Joshua the elder is the grandfather of your Joshua. Unfortunately, none of the boys has a Norman or Leonard living with him in 1901.
1901: RG13/3923 38 14
15 Duxbury Street, Darwen Thurston Leach, head, 31, Moulder (?) Clay, b. Hoddlesden
Rhoda, wife, 31, b. Darwen
Victoria, dau, 3, b. Darwen
Marsden, son, 1, b. Darwen
RG13/3921 125 28
Darwen, 25 London Terrace Joshua Leach, head, Sanitary pipe (sthg), b. Darwen Hoddlesden
Alice, wife, 29, Cotton weaver, b. Bethorn
I think you would need to get hold of Joshua's birth cert to sort out who he actually belongs to.
FreeBMD has the following birth:
December quarter 1894
Registration district Blackburn
Volume 8e page 457
I also see the births of
Norman Leach registered in December quarter 1902
Leonard Leach, September quarter 1901
both in Blackburn - which would explain why I can't see them in 1901.
Sorry I'm not able do do more for the moment. But please come back to me once you have the cert - we'll certainly be able to trace them a little further back one we have his parent's names.
Tanja