Hello maryjanenewbie-
The very short answer to your question is yes, the pots they are in will accomodate the plants you have in them. However, they will not get to be 4 or 5 feet tall for several reasons.
First off, you are growing an indica dominant strain, correct? Switching to 12/12 at 18" under a 400 watt light, in the size pot they are in, they won't reach 4' during flower.
Put them in a bigger pot, say 5 gallon, and they will grow bigger and healthier... but you won't have enough light from a single 400 watt bulb to effectively light the canopy of 7 plants. The 5 gallon pots will take up too much space and spread them out too far.
Have they shown sex yet? What schedule are you on, 24/0 or 18/6? When I grow indicas, they usually show sex at 6 weeks on an 18/6 schedule. Perhaps that may make your decisions easier if you have to cull a few males.
4 plants under a 400 watt light in 5 gallon pails (I use 24 quart kitchen trash cans with holes in the bottom- they have handles, makes them easier to move if need be) should grow very nicely under a 400 watter.
IMHO, as it stands now, your plants will most likely end up root bound.
Just my .02. Good luck.
