Good morning W., I am chuckling over here because as I am reading this, I too, am up with my 11 month old son at 5 a.m. SIGH! He sounds alot like your son, he takes two day time naps, about 30-60 mins(if we are lucky)LOL! My son usually goes to sleep around 8:30 or 9, will wake again around 11. After that it is hit and miss, sometimes he wakes at 1 or 2, sometimes he wakes at 3 or 4. But he is always up for the day at 5 or 6. When he wakes before 5 or 6 I usually sleep nurse him in our bed(make sure you put him on the inside of the bed between you and your husband, so he does not fall off.) I know how hard this is for you, this is actually baby number 3 for me to nurse. Hang in there, hopefully it will get better in a few months.
Actually, my son just started sleeping thru the night this past week. He has not made a "habit" of it yet, but last week he did sleep from 9 until 6. WHOOHOO!! He did this for two nights last week, hopefully he will do it more often.
Sorry I do not have more advice, other than try not to let him sleep past 5 pm, until he goes to bed for the night. Maybe you might be comforted to know there is another mommy out there right now dealing with the exact same thing LOL, you are not alone...I feel for you. It will get better, maybe not as soon as we like, but I am sure he will be sleeping thru the night in a few more months. Take care.