I love Leo and I don't think the endings would bother me since the LN is so many syllables. I think Sebastian + 4 syllable LN would be a big name for a little guy to learn to spell:)
I prefer Leo. I don't think the same ending is a big deal since your last name is so long. I agree with pp that Sebastian plus a long last name is a little much for me
Re: Down to the final 2 choices
DD1 born 5/24/10.
Missed M/C at 14 wks Feb 2012.
DD2 born 5/14/13.
Missed M/C at 9 wks July 2015.
Though Leopold, nn Leo would be amazing. Don't care for Leo as a given name.
Silas. Theodore. Henry.