Hello all,
I've started DM'ing a group using 3.5 rules / guidelines which I am somewhat new to. I'm learning and do like the system but seems to leave some grey areas. So, I would like to make sure that I / we the group were following the rules of grappling since it does seem to come into play much more of late. Here is a short version on two of the battles that I wasn't sure on even after reading up on grapple in the PH1 and DMG. Maybe I'm just missing the boat and you all can catch me up.

A fighter was surrounded by kobolds and 2 dire weasel's.. yeah.. not a good situation. Anyhow, the dire weasel had latched on with the Attach (Ex) feat and the Dire weasel won the opposed after one round and perform the Blood Drain 1d4 Constitution dmg per round that the weasel is attached. So, I have two questions for this battle. #1 - While attached does the Dire weasel also cause damage in addition to the Blood drain? #2 - The other Dire Weasel and kobolds still surrounding the fighter do they attack w/o chance of hitting the attached Dire weasels.. how would that go? and the other dire weasel, could it attack and also Attach(Ex) and Blood drain. I'm sure I may have went real easy on the the fighter cause I wasn't sure so the whole time the Dire weasel was Attached I didnt have the others attacking because of chance of hitting the dire weasel. Just wasn't sure on the rules with this so if I was wrong.. we chalk it up to gift for the gods.. lol

Same game session different battle. The party is now fighting Ankheg's which have Improved Grapple (Ex)
The Druid ended up getting bit and and grappled due to losing the opposed check. And stayed there for two rounds. My question on this part is while in the mandibles of the Ankheg does the PC take damage and how much? I wasn't sure after reading the grapple rules because it seem to be explaining two humanoids fighting.

And I guess one more question..
When the druids was attacked she was casting a spell which she had to roll a concentration check vs DC + damage. But because of being grappled after the bite does she roll another concentration because of the struggle (opposed check) to dismiss the grapple.

So, thank you in advance and I'm looking forward to the advice.