K.I.
Have you bought your daughter a sit in "bouncy thing"? Not the ones for the little babies but the ones that they sit/stand in with toys all around...the saucer things? My kids loved those! This might not help seeing how you are also asking how to keep your son and his toys out of the living room but my favorite thing was putting down a huge blanket and encircling my child with all kinds of toys! This usually keeps them busy enough for at least a little bit of time?? I also utilized the high chair a lot, while I was in the kitchen...just give her some snacks to eat or play with :) or some toys and a sippy cup? Also, this is messy but works well- I used to strip my kids down to the diaper and give them some baby food in a bowl and their own spoon and allow them to try and feed themselves...they love this and can spend a long time "playing" with their food and spoon! Just make sure you move them away from the wall or anything they can touch to try and minimize the mess some:) Then just take 'em out and put them in the bath and do a quick wipe down of the high chair immediately to lesson the clean up!
Sorry I have no advice about your son when company comes over...mine were always in the living room with all there toys (I have one of those living room that is lined with toys and toy boxes)...I just barely have gotten to the point with mine where I can send them downstairs or to their room to play when the adults need some time...and mine are 6, 4 and 2...and they have each other, which helps A LOT!
Hope some of this helps! All 3 of mine were "momma freaks" and I know how much patience (for the holding) and imagination (for creative ideas and fun w/out you) it takes to get thru the first year and a half!