Yes, ds could hold his own TT bottles - he held it with both hands, so it being wide didn't matter. Whether or not you should let him do it for himself - well, that's a whole other argument, but thought I'd just answer on the technical side of it.
I used these bottles but DS found them quite hard to hold and could'nt find any sort of adapter, but you can get a Cup which is similair to the bottle with a spout instead or I bought the Avent Magic Cups which are coloured and have a removable handle on them and they come with spouts but can be used with a normal teat if baby needs time to adjust to the cup.
My 10.5 month old cannot/won't hold them (although he can use a cup very well) but he is also bf so not sure if he is more 'passive' in terms of being milk fed! My older kids were bottle fed and held their own bottles much earlier but we used the thin bottles.
My DS held his bottle from about 4 months with both hands. Wasnt a problem. drank the whole thing down. Some of them can, some cant. But I dont think the width of the bottle should be an issue for them. I dont think they really need handles at this point either.