You are the only one who can decide if you're capable and ready to raise 2 at the same time...it can be work...but for us it has worked out fine.
We had Jo for about 6 months before we got Riley so I was training them both at the same time and it worked out great. We just bought 11 week old sisters and their training is going great...except for that little 'revenge poop' in the dining room last night
Yes, it can be work but there are advantages to it...they snuggle up and sleep all night with no crying, they have someone their size and age to play with and...well...they're sisters and you just can't break up sisters! Yes, there are days when I wonder about my sanity but for the most part...we're having a blast and I wouldn't change a thing! Well, except that I'll be adding another one soon!